Block on rough horizontal surface
Normal reaction balances weight when there is no vertical acceleration.
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F5
CLASS 11 PHYSICS • LAWS OF MOTION
Friction and Applications
Master static friction, limiting friction, kinetic friction, angle of repose, rolling friction, graphs and exam-level applications.
CBSENEETJEE MainJEE AdvancedIBIGCSEA-Level
Section 1
Friction
Friction is a contact force parallel to the surfaces in contact. It opposes relative motion or tendency of relative motion and exists because microscopic roughness interlocks at contact points.
Applied force and friction direction
When a force tries to move the block right, friction acts left if tendency is right.
Friction opposing relative motion
Friction is decided by relative motion at contact, not always by velocity of the body.
Contact surfaces
Real surfaces have microscopic hills and valleys that produce resistance.
Section 2
Static Friction
Static friction acts when surfaces do not slide. It is self-adjusting and can take any value from zero to limiting friction.
0 ≤ fs ≤ flim
Pushing a heavy box
For a small push, static friction equals the push and the box stays at rest.
Object at rest on rough surface
If there is no tendency to slide, static friction can be zero.
Walking
Static friction on the foot acts forward and helps walking.
Section 3
Limiting Friction
Limiting friction is the maximum static friction just before sliding begins.
flim = μsN
Force diagram
At impending motion, static friction has reached its greatest value.
Common mistake
Students often use limiting friction even when the body is not about to move. First find required static friction, then compare with μsN.
Section 4
Kinetic Friction
Kinetic friction acts during sliding and is directed opposite relative sliding.
fk = μkN
μk < μs
Sliding friction
Once the block slides, use kinetic friction.
Direction
If the block slides right over the surface, friction on it acts left.
Section 5
Coefficient of Friction
The coefficient of friction μ is a unitless ratio of friction to normal reaction. It depends on nature of surfaces and not on apparent area of contact in ideal theory.
μ = f / N
| Surface Pair | Approximate Friction Level | Physical Meaning |
|---|---|---|
| Polished metal on metal | Low | Easy sliding |
| Rubber tyre on dry road | High | Strong grip |
| Wood on wood | Medium | Noticeable resistance |
| Ice on ice | Very low | Slipping likely |
| Ball bearings | Very low rolling friction | Smooth rotation |
Section 6
Angle of Friction
The resultant reaction R is the vector sum of normal reaction N and friction f. The angle between R and N is angle of friction λ.
tan λ = f / N
At limiting friction: tan λ = μ
λ = tan-1μ
Section 7
Angle of Repose
Angle of repose is the angle of incline at which a body just starts sliding down. At this point friction is limiting.
mg sin θ = f
N = mg cos θ
At limiting friction, f = μN
mg sin θ = μmg cos θ
tan θ = μ
Thus angle of repose equals angle of friction.
Section 8
Rolling Friction
Rolling friction is smaller than sliding friction because deformation and microscopic sliding are reduced. Wheels, bearings and tyres use rolling contact.
Rolling wheel
Wheels reduce energy loss by rolling instead of sliding.
Bearings
Ball bearings reduce friction between moving machine parts.
Tyres
Tyres need enough friction for grip, braking and turning.
Section 9
Important Graphs
Friction vs Applied Force
Static friction rises with applied force up to limiting friction. During sliding, kinetic friction is lower and approximately constant.
Static friction region
Static friction rises with applied force up to limiting friction. During sliding, kinetic friction is lower and approximately constant.
Limiting friction point
Static friction rises with applied force up to limiting friction. During sliding, kinetic friction is lower and approximately constant.
Kinetic friction region
Static friction rises with applied force up to limiting friction. During sliding, kinetic friction is lower and approximately constant.
f vs N graph
Static friction rises with applied force up to limiting friction. During sliding, kinetic friction is lower and approximately constant.
μ comparison graph
Static friction rises with applied force up to limiting friction. During sliding, kinetic friction is lower and approximately constant.
Inclined plane friction graph
Static friction rises with applied force up to limiting friction. During sliding, kinetic friction is lower and approximately constant.
Section 10
Applications of Friction
Walking
Concept: Static friction from the ground pushes the foot forward.
Diagram: The sketch shows the actual application, not a generic block diagram.
Friction direction: Forward on the foot; backward on the ground.
Exam tip: Decide tendency of relative motion at the contact first.
Writing with pen
Concept: Friction between pen tip and paper lets ink form visible marks.
Diagram: The sketch shows the actual application, not a generic block diagram.
Friction direction: Opposite the pen tip sliding over paper.
Exam tip: Decide tendency of relative motion at the contact first.
Brakes
Concept: Brake pads use friction to reduce wheel rotation and stop the vehicle.
Diagram: The sketch shows the actual application, not a generic block diagram.
Friction direction: Opposite wheel motion at the brake contact.
Exam tip: Decide tendency of relative motion at the contact first.
Tyres
Concept: Tyre-road friction gives grip for acceleration, braking and turning.
Diagram: The sketch shows the actual application, not a generic block diagram.
Friction direction: At road contact, opposite relative slipping tendency.
Exam tip: Decide tendency of relative motion at the contact first.
Ladder against wall
Concept: Friction at floor or wall prevents the ladder from slipping.
Diagram: The sketch shows the actual application, not a generic block diagram.
Friction direction: At floor, usually toward the wall for a ladder tending to slip outward.
Exam tip: Decide tendency of relative motion at the contact first.
Belt drive
Concept: Friction between belt and pulley transfers rotation without slipping.
Diagram: The sketch shows the actual application, not a generic block diagram.
Friction direction: Along belt contact, opposing slip between belt and pulley.
Exam tip: Decide tendency of relative motion at the contact first.
Rope and pulley
Concept: Friction can change tension on two sides of a rough pulley or support grip.
Diagram: The sketch shows the actual application, not a generic block diagram.
Friction direction: Along rope contact, opposite relative sliding.
Exam tip: Decide tendency of relative motion at the contact first.
Banked roads basic connection
Concept: Friction assists or opposes side slip on a banked road depending on speed.
Diagram: The sketch shows the actual application, not a generic block diagram.
Friction direction: Up or down the bank after checking tendency.
Exam tip: Decide tendency of relative motion at the contact first.
Screws and nails
Concept: Friction in threads and surfaces helps screws and nails hold tightly.
Diagram: The sketch shows the actual application, not a generic block diagram.
Friction direction: Along contact thread, resisting loosening/sliding.
Exam tip: Decide tendency of relative motion at the contact first.
Rolling wheels
Concept: Rolling friction is smaller than sliding friction, so wheels reduce effort.
Diagram: The sketch shows the actual application, not a generic block diagram.
Friction direction: Opposes rolling motion due to deformation at contact.
Exam tip: Decide tendency of relative motion at the contact first.
Section 11
High-Quality Numericals
CBSE NumericalShow Answer
Question: A 5 kg block on rough ground has μs=0.4. Find least force to start motion.
Free Body Diagram: Draw mg downward, N perpendicular to contact, applied force along its direction and friction opposite relative motion or tendency.
Given: m=5 kg, μs=0.4, g=10
Formula: flim=μsN
Calculation: N=50 N, f=0.4 x 50=20 N
Final Answer: 20 N
Exam Tip: Use limiting friction only at impending motion.
Common Mistake: Do not use kinetic friction before motion starts.
NEET NumericalShow Answer
Question: A body starts sliding when incline angle is 37 degree. Find μ.
Free Body Diagram: Draw mg downward, N perpendicular to contact, applied force along its direction and friction opposite relative motion or tendency.
Given: θ=37 degree
Formula: μ=tanθ
Calculation: tan37 degree=3/4
Final Answer: 0.75
Exam Tip: Angle of repose gives coefficient directly.
Common Mistake: Do not use sinθ as coefficient.
JEE Main NumericalShow Answer
Question: A 2 kg block is pulled by 15 N on a rough floor, μk=0.25. Find acceleration.
Free Body Diagram: Draw mg downward, N perpendicular to contact, applied force along its direction and friction opposite relative motion or tendency.
Given: m=2 kg, F=15 N, μk=0.25
Formula: F-μkmg=ma
Calculation: friction=5 N, net=10 N, a=5
Final Answer: 5 m/s2
Exam Tip: Subtract friction from applied force.
Common Mistake: Do not put friction in direction of motion.
JEE Advanced NumericalShow Answer
Question: Two blocks move together without slipping. What friction model is used?
Free Body Diagram: Draw mg downward, N perpendicular to contact, applied force along its direction and friction opposite relative motion or tendency.
Given: No relative slip
Formula: Use static friction and common acceleration constraint
Calculation: Write FBD of each block and solve static friction required. Check f_s ≤ &mu_s N.
Final Answer: Static friction, not limiting unless at threshold.
Exam Tip: Check maximum after solution.
Common Mistake: Do not assume f_s=&mu_sN.
IB NumericalShow Answer
Question: Explain why static friction is self-adjusting.
Free Body Diagram: Draw mg downward, N perpendicular to contact, applied force along its direction and friction opposite relative motion or tendency.
Given: Body at rest
Formula: 0 ≤ f_s ≤ f_lim
Calculation: It equals the required opposing force until maximum is reached.
Final Answer: Static friction has a range.
Exam Tip: State the range clearly.
Common Mistake: Do not give only one value.
IGCSE NumericalShow Answer
Question: Why do tyres need friction?
Free Body Diagram: Draw mg downward, N perpendicular to contact, applied force along its direction and friction opposite relative motion or tendency.
Given: Tyre-road contact
Formula: Grip due to friction
Calculation: Friction prevents slipping and helps acceleration, braking and turning.
Final Answer: Tyres need sufficient friction.
Exam Tip: Application questions need direction and purpose.
Common Mistake: Do not call friction always harmful.
A-Level NumericalShow Answer
Question: Derive angle of friction at limiting condition.
Free Body Diagram: Draw mg downward, N perpendicular to contact, applied force along its direction and friction opposite relative motion or tendency.
Given: f=μN
Formula: tanλ=f/N
Calculation: tanλ=μ so λ=tan^-1μ
Final Answer: λ=tan-1μ
Exam Tip: Use resultant reaction diagram.
Common Mistake: Do not measure angle from surface.
Section 12
NEET Question Bank
NEET Exam-style Question 1Show Answer
Question: NEET 1: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
NEET Exam-style Question 2Show Answer
Question: NEET 2: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
NEET Exam-style Question 3Show Answer
Question: NEET 3: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
NEET Exam-style Question 4Show Answer
Question: NEET 4: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
NEET Exam-style Question 5Show Answer
Question: NEET 5: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
NEET Exam-style Question 6Show Answer
Question: NEET 6: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
NEET Exam-style Question 7Show Answer
Question: NEET 7: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
NEET Exam-style Question 8Show Answer
Question: NEET 8: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
NEET Exam-style Question 9Show Answer
Question: NEET 9: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
NEET Exam-style Question 10Show Answer
Question: NEET 10: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
NEET Exam-style Question 11Show Answer
Question: NEET 11: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
NEET Exam-style Question 12Show Answer
Question: NEET 12: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
NEET Exam-style Question 13Show Answer
Question: NEET 13: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
NEET Exam-style Question 14Show Answer
Question: NEET 14: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
NEET Exam-style Question 15Show Answer
Question: NEET 15: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
NEET Exam-style Question 16Show Answer
Question: NEET 16: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
NEET Exam-style Question 17Show Answer
Question: NEET 17: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
NEET Exam-style Question 18Show Answer
Question: NEET 18: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
NEET Exam-style Question 19Show Answer
Question: NEET 19: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
NEET Exam-style Question 20Show Answer
Question: NEET 20: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
NEET Exam-style Question 21Show Answer
Question: NEET 21: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
NEET Exam-style Question 22Show Answer
Question: NEET 22: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
NEET Exam-style Question 23Show Answer
Question: NEET 23: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
NEET Exam-style Question 24Show Answer
Question: NEET 24: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
NEET Exam-style Question 25Show Answer
Question: NEET 25: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
NEET Exam-style Question 26Show Answer
Question: NEET 26: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
NEET Exam-style Question 27Show Answer
Question: NEET 27: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
NEET Exam-style Question 28Show Answer
Question: NEET 28: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
NEET Exam-style Question 29Show Answer
Question: NEET 29: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
NEET Exam-style Question 30Show Answer
Question: NEET 30: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
NEET Exam-style Question 31Show Answer
Question: NEET 31: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
NEET Exam-style Question 32Show Answer
Question: NEET 32: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
NEET Exam-style Question 33Show Answer
Question: NEET 33: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
NEET Exam-style Question 34Show Answer
Question: NEET 34: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
NEET Exam-style Question 35Show Answer
Question: NEET 35: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
NEET Exam-style Question 36Show Answer
Question: NEET 36: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
NEET Exam-style Question 37Show Answer
Question: NEET 37: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
NEET Exam-style Question 38Show Answer
Question: NEET 38: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
NEET Exam-style Question 39Show Answer
Question: NEET 39: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
NEET Exam-style Question 40Show Answer
Question: NEET 40: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
NEET Exam-style Question 41Show Answer
Question: NEET 41: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
NEET Exam-style Question 42Show Answer
Question: NEET 42: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
NEET Exam-style Question 43Show Answer
Question: NEET 43: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
NEET Exam-style Question 44Show Answer
Question: NEET 44: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
NEET Exam-style Question 45Show Answer
Question: NEET 45: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
NEET Exam-style Question 46Show Answer
Question: NEET 46: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
NEET Exam-style Question 47Show Answer
Question: NEET 47: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
NEET Exam-style Question 48Show Answer
Question: NEET 48: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
NEET Exam-style Question 49Show Answer
Question: NEET 49: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
NEET Exam-style Question 50Show Answer
Question: NEET 50: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
Section 13
JEE Main Question Bank
JEE Main Exam-style Question 1Show Answer
Question: JEE Main 1: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 2Show Answer
Question: JEE Main 2: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 3Show Answer
Question: JEE Main 3: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 4Show Answer
Question: JEE Main 4: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 5Show Answer
Question: JEE Main 5: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 6Show Answer
Question: JEE Main 6: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 7Show Answer
Question: JEE Main 7: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 8Show Answer
Question: JEE Main 8: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 9Show Answer
Question: JEE Main 9: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 10Show Answer
Question: JEE Main 10: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 11Show Answer
Question: JEE Main 11: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 12Show Answer
Question: JEE Main 12: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 13Show Answer
Question: JEE Main 13: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 14Show Answer
Question: JEE Main 14: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 15Show Answer
Question: JEE Main 15: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 16Show Answer
Question: JEE Main 16: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 17Show Answer
Question: JEE Main 17: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 18Show Answer
Question: JEE Main 18: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 19Show Answer
Question: JEE Main 19: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 20Show Answer
Question: JEE Main 20: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 21Show Answer
Question: JEE Main 21: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 22Show Answer
Question: JEE Main 22: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 23Show Answer
Question: JEE Main 23: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 24Show Answer
Question: JEE Main 24: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 25Show Answer
Question: JEE Main 25: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 26Show Answer
Question: JEE Main 26: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 27Show Answer
Question: JEE Main 27: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 28Show Answer
Question: JEE Main 28: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 29Show Answer
Question: JEE Main 29: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 30Show Answer
Question: JEE Main 30: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 31Show Answer
Question: JEE Main 31: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 32Show Answer
Question: JEE Main 32: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 33Show Answer
Question: JEE Main 33: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 34Show Answer
Question: JEE Main 34: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 35Show Answer
Question: JEE Main 35: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 36Show Answer
Question: JEE Main 36: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 37Show Answer
Question: JEE Main 37: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 38Show Answer
Question: JEE Main 38: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 39Show Answer
Question: JEE Main 39: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 40Show Answer
Question: JEE Main 40: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 41Show Answer
Question: JEE Main 41: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 42Show Answer
Question: JEE Main 42: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 43Show Answer
Question: JEE Main 43: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 44Show Answer
Question: JEE Main 44: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 45Show Answer
Question: JEE Main 45: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 46Show Answer
Question: JEE Main 46: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 47Show Answer
Question: JEE Main 47: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 48Show Answer
Question: JEE Main 48: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 49Show Answer
Question: JEE Main 49: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
JEE Main Exam-style Question 50Show Answer
Question: JEE Main 50: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
Section 14
JEE Advanced Question Bank
JEE Advanced Exam-style Question 1Show Answer
Question: JEE Advanced 1: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 2Show Answer
Question: JEE Advanced 2: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 3Show Answer
Question: JEE Advanced 3: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 4Show Answer
Question: JEE Advanced 4: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 5Show Answer
Question: JEE Advanced 5: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 6Show Answer
Question: JEE Advanced 6: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 7Show Answer
Question: JEE Advanced 7: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 8Show Answer
Question: JEE Advanced 8: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 9Show Answer
Question: JEE Advanced 9: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 10Show Answer
Question: JEE Advanced 10: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 11Show Answer
Question: JEE Advanced 11: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 12Show Answer
Question: JEE Advanced 12: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 13Show Answer
Question: JEE Advanced 13: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 14Show Answer
Question: JEE Advanced 14: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 15Show Answer
Question: JEE Advanced 15: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 16Show Answer
Question: JEE Advanced 16: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 17Show Answer
Question: JEE Advanced 17: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 18Show Answer
Question: JEE Advanced 18: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 19Show Answer
Question: JEE Advanced 19: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 20Show Answer
Question: JEE Advanced 20: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 21Show Answer
Question: JEE Advanced 21: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 22Show Answer
Question: JEE Advanced 22: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 23Show Answer
Question: JEE Advanced 23: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 24Show Answer
Question: JEE Advanced 24: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 25Show Answer
Question: JEE Advanced 25: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 26Show Answer
Question: JEE Advanced 26: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 27Show Answer
Question: JEE Advanced 27: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 28Show Answer
Question: JEE Advanced 28: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 29Show Answer
Question: JEE Advanced 29: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 30Show Answer
Question: JEE Advanced 30: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 31Show Answer
Question: JEE Advanced 31: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 32Show Answer
Question: JEE Advanced 32: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 33Show Answer
Question: JEE Advanced 33: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 34Show Answer
Question: JEE Advanced 34: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 35Show Answer
Question: JEE Advanced 35: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 36Show Answer
Question: JEE Advanced 36: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 37Show Answer
Question: JEE Advanced 37: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 38Show Answer
Question: JEE Advanced 38: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 39Show Answer
Question: JEE Advanced 39: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 40Show Answer
Question: JEE Advanced 40: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 41Show Answer
Question: JEE Advanced 41: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 42Show Answer
Question: JEE Advanced 42: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 43Show Answer
Question: JEE Advanced 43: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 44Show Answer
Question: JEE Advanced 44: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 45Show Answer
Question: JEE Advanced 45: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 46Show Answer
Question: JEE Advanced 46: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 47Show Answer
Question: JEE Advanced 47: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 48Show Answer
Question: JEE Advanced 48: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 49Show Answer
Question: JEE Advanced 49: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
JEE Advanced Exam-style Question 50Show Answer
Question: JEE Advanced 50: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
Section 15
IB / IGCSE / A-Level Questions
IB Questions
IB Exam-style Question 1Show Answer
Question: IB 1: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 2Show Answer
Question: IB 2: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 3Show Answer
Question: IB 3: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 4Show Answer
Question: IB 4: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 5Show Answer
Question: IB 5: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 6Show Answer
Question: IB 6: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 7Show Answer
Question: IB 7: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 8Show Answer
Question: IB 8: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 9Show Answer
Question: IB 9: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 10Show Answer
Question: IB 10: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 11Show Answer
Question: IB 11: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 12Show Answer
Question: IB 12: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 13Show Answer
Question: IB 13: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 14Show Answer
Question: IB 14: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 15Show Answer
Question: IB 15: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 16Show Answer
Question: IB 16: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 17Show Answer
Question: IB 17: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 18Show Answer
Question: IB 18: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 19Show Answer
Question: IB 19: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 20Show Answer
Question: IB 20: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 21Show Answer
Question: IB 21: A force P is applied but block stays at rest. Find friction.
Correct Answer: f_s=P if P is less than limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 22Show Answer
Question: IB 22: A block tends to slide down an incline. Direction of friction?
Correct Answer: Up the plane.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 23Show Answer
Question: IB 23: A block slides on floor. Which coefficient is used?
Correct Answer: Use μk.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 24Show Answer
Question: IB 24: What is slope of f versus N graph?
Correct Answer: Coefficient of friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IB Exam-style Question 25Show Answer
Question: IB 25: Why is f=μsN not always valid?
Correct Answer: It is valid only at limiting friction.
Detailed Explanation: Draw FBD, decide contact condition, then apply static, limiting or kinetic friction.
IGCSE Questions
IGCSE Exam-style Question 1Show Answer
Question: IGCSE 1: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
IGCSE Exam-style Question 2Show Answer
Question: IGCSE 2: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
IGCSE Exam-style Question 3Show Answer
Question: IGCSE 3: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
IGCSE Exam-style Question 4Show Answer
Question: IGCSE 4: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
IGCSE Exam-style Question 5Show Answer
Question: IGCSE 5: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
IGCSE Exam-style Question 6Show Answer
Question: IGCSE 6: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
IGCSE Exam-style Question 7Show Answer
Question: IGCSE 7: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
IGCSE Exam-style Question 8Show Answer
Question: IGCSE 8: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
IGCSE Exam-style Question 9Show Answer
Question: IGCSE 9: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
IGCSE Exam-style Question 10Show Answer
Question: IGCSE 10: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
IGCSE Exam-style Question 11Show Answer
Question: IGCSE 11: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
IGCSE Exam-style Question 12Show Answer
Question: IGCSE 12: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
IGCSE Exam-style Question 13Show Answer
Question: IGCSE 13: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
IGCSE Exam-style Question 14Show Answer
Question: IGCSE 14: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
IGCSE Exam-style Question 15Show Answer
Question: IGCSE 15: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
IGCSE Exam-style Question 16Show Answer
Question: IGCSE 16: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
IGCSE Exam-style Question 17Show Answer
Question: IGCSE 17: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
IGCSE Exam-style Question 18Show Answer
Question: IGCSE 18: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
IGCSE Exam-style Question 19Show Answer
Question: IGCSE 19: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
IGCSE Exam-style Question 20Show Answer
Question: IGCSE 20: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
IGCSE Exam-style Question 21Show Answer
Question: IGCSE 21: Static friction is self-adjusting because?
Options: (A) it changes as required (B) it is always μsN (C) it acts along velocity (D) it is zero
Correct Answer: A
Detailed Explanation: Static friction takes the required value up to limiting friction.
IGCSE Exam-style Question 22Show Answer
Question: IGCSE 22: At impending motion on horizontal surface friction is?
Options: (A) 0 (B) μsN (C) μkN (D) mg
Correct Answer: B
Detailed Explanation: Just before motion, static friction is limiting.
IGCSE Exam-style Question 23Show Answer
Question: IGCSE 23: Sliding friction is?
Options: (A) μsN (B) μkN (C) ma (D) zero
Correct Answer: B
Detailed Explanation: During sliding use kinetic friction.
IGCSE Exam-style Question 24Show Answer
Question: IGCSE 24: Angle of repose relation is?
Options: (A) sinθ=μ (B) cosθ=μ (C) tanθ=μ (D) θ=μ
Correct Answer: C
Detailed Explanation: Resolve forces on incline.
IGCSE Exam-style Question 25Show Answer
Question: IGCSE 25: Friction on walking foot is usually?
Options: (A) backward (B) forward (C) zero (D) downward
Correct Answer: B
Detailed Explanation: The ground exerts forward static friction on the foot.
A-Level Questions
A-Level Exam-style Question 1Show Answer
Question: A-Level 1: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 2Show Answer
Question: A-Level 2: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 3Show Answer
Question: A-Level 3: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 4Show Answer
Question: A-Level 4: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 5Show Answer
Question: A-Level 5: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 6Show Answer
Question: A-Level 6: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 7Show Answer
Question: A-Level 7: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 8Show Answer
Question: A-Level 8: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 9Show Answer
Question: A-Level 9: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 10Show Answer
Question: A-Level 10: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 11Show Answer
Question: A-Level 11: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 12Show Answer
Question: A-Level 12: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 13Show Answer
Question: A-Level 13: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 14Show Answer
Question: A-Level 14: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 15Show Answer
Question: A-Level 15: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 16Show Answer
Question: A-Level 16: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 17Show Answer
Question: A-Level 17: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 18Show Answer
Question: A-Level 18: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 19Show Answer
Question: A-Level 19: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 20Show Answer
Question: A-Level 20: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 21Show Answer
Question: A-Level 21: Block over block starts slipping. Which friction before and after slip?
Correct Answer: Before slipping use static friction; after slipping use kinetic friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 22Show Answer
Question: A-Level 22: Wedge with friction accelerates. How decide direction?
Correct Answer: Use pseudo force and relative tendency along the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 23Show Answer
Question: A-Level 23: Maximum force before block moves up rough incline?
Correct Answer: Use limiting friction down the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 24Show Answer
Question: A-Level 24: Minimum force to prevent sliding down?
Correct Answer: Use limiting friction up the plane.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
A-Level Exam-style Question 25Show Answer
Question: A-Level 25: Pulley with rough table block: first step?
Correct Answer: Write string constraint and FBDs including friction.
Detailed Explanation: Advanced friction needs case checking. Assume a tendency, draw friction opposite, solve, then verify sign and limit.
Section 16
Assertion Reason
Assertion-Reason 1Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 2Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 3Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 4Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 5Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 6Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 7Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 8Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 9Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 10Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 11Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 12Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 13Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 14Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 15Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 16Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 17Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 18Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 19Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 20Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 21Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 22Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 23Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 24Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 25Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 26Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 27Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 28Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 29Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Assertion-Reason 30Show Answer
Question: Assertion: Friction law depends on contact condition. Reason: Static, limiting and kinetic friction have different meanings.
Answer: Both are true and the reason explains the assertion.
Explanation: Identify the state of contact before using any formula.
Section 17
Case Study Questions
1. Walking on road
Passage: In walking on road, friction controls grip, slipping and possible acceleration. Draw the FBD first and decide relative tendency at every contact.
Case 1.1Show Answer
Question: In walking on road, what should be checked before writing friction equation 1?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 1.2Show Answer
Question: In walking on road, what should be checked before writing friction equation 2?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 1.3Show Answer
Question: In walking on road, what should be checked before writing friction equation 3?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 1.4Show Answer
Question: In walking on road, what should be checked before writing friction equation 4?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
2. Car braking
Passage: In car braking, friction controls grip, slipping and possible acceleration. Draw the FBD first and decide relative tendency at every contact.
Case 2.1Show Answer
Question: In car braking, what should be checked before writing friction equation 1?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 2.2Show Answer
Question: In car braking, what should be checked before writing friction equation 2?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 2.3Show Answer
Question: In car braking, what should be checked before writing friction equation 3?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 2.4Show Answer
Question: In car braking, what should be checked before writing friction equation 4?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
3. Box on rough floor
Passage: In box on rough floor, friction controls grip, slipping and possible acceleration. Draw the FBD first and decide relative tendency at every contact.
Case 3.1Show Answer
Question: In box on rough floor, what should be checked before writing friction equation 1?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 3.2Show Answer
Question: In box on rough floor, what should be checked before writing friction equation 2?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 3.3Show Answer
Question: In box on rough floor, what should be checked before writing friction equation 3?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 3.4Show Answer
Question: In box on rough floor, what should be checked before writing friction equation 4?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
4. Block on inclined plane
Passage: In block on inclined plane, friction controls grip, slipping and possible acceleration. Draw the FBD first and decide relative tendency at every contact.
Case 4.1Show Answer
Question: In block on inclined plane, what should be checked before writing friction equation 1?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 4.2Show Answer
Question: In block on inclined plane, what should be checked before writing friction equation 2?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 4.3Show Answer
Question: In block on inclined plane, what should be checked before writing friction equation 3?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 4.4Show Answer
Question: In block on inclined plane, what should be checked before writing friction equation 4?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
5. Ladder on rough wall
Passage: In ladder on rough wall, friction controls grip, slipping and possible acceleration. Draw the FBD first and decide relative tendency at every contact.
Case 5.1Show Answer
Question: In ladder on rough wall, what should be checked before writing friction equation 1?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 5.2Show Answer
Question: In ladder on rough wall, what should be checked before writing friction equation 2?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 5.3Show Answer
Question: In ladder on rough wall, what should be checked before writing friction equation 3?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 5.4Show Answer
Question: In ladder on rough wall, what should be checked before writing friction equation 4?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
6. Rolling wheel
Passage: In rolling wheel, friction controls grip, slipping and possible acceleration. Draw the FBD first and decide relative tendency at every contact.
Case 6.1Show Answer
Question: In rolling wheel, what should be checked before writing friction equation 1?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 6.2Show Answer
Question: In rolling wheel, what should be checked before writing friction equation 2?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 6.3Show Answer
Question: In rolling wheel, what should be checked before writing friction equation 3?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 6.4Show Answer
Question: In rolling wheel, what should be checked before writing friction equation 4?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
7. Friction in connected bodies
Passage: In friction in connected bodies, friction controls grip, slipping and possible acceleration. Draw the FBD first and decide relative tendency at every contact.
Case 7.1Show Answer
Question: In friction in connected bodies, what should be checked before writing friction equation 1?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 7.2Show Answer
Question: In friction in connected bodies, what should be checked before writing friction equation 2?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 7.3Show Answer
Question: In friction in connected bodies, what should be checked before writing friction equation 3?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Case 7.4Show Answer
Question: In friction in connected bodies, what should be checked before writing friction equation 4?
Answer: Check whether contact is static, limiting or sliding. Then choose f_s, f_lim or f_k.
Detailed explanation: Friction direction is decided by relative tendency, not by habit.
Section 18
Common Student Mistakes
Assuming friction always equals μN
Fix: Draw FBD first, identify contact condition, decide relative tendency, then apply the correct formula.
Confusing static and limiting friction
Fix: Draw FBD first, identify contact condition, decide relative tendency, then apply the correct formula.
Wrong friction direction
Fix: Draw FBD first, identify contact condition, decide relative tendency, then apply the correct formula.
Using μk instead of μs
Fix: Draw FBD first, identify contact condition, decide relative tendency, then apply the correct formula.
Forgetting normal reaction changes on inclined plane
Fix: Draw FBD first, identify contact condition, decide relative tendency, then apply the correct formula.
Taking friction up or down the incline without checking tendency
Fix: Draw FBD first, identify contact condition, decide relative tendency, then apply the correct formula.
Ignoring friction in connected-body equations
Fix: Draw FBD first, identify contact condition, decide relative tendency, then apply the correct formula.
Misreading friction vs applied force graph
Fix: Draw FBD first, identify contact condition, decide relative tendency, then apply the correct formula.
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Friction explained
Static friction explained
Limiting friction explained
Kinetic friction explained
Coefficient of friction explained
Angle of friction derived
Angle of repose derived
Rolling friction included
Important graphs included
Applications included
High-quality SVG diagrams included
NEET questions included
JEE Main questions included
JEE Advanced questions included
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