50 Conceptual Questions with Answers

Power, Linear Acceleration and Impulse

1. What is power in mechanics?
   Answer: Power is the rate of doing work or the rate of energy transfer.

2. Write the basic formula of power.
   Answer: (P = \frac{dW}{dt})

3. How is instantaneous power related to force and velocity?
   Answer: Instantaneous power is (P = \vec F \cdot \vec v).

4. When is power maximum for a given force and speed?
   Answer: Power is maximum when force and velocity are in the same direction.

5. When is power zero even if force is acting?
   Answer: Power is zero when force is perpendicular to velocity.

6. Can power be negative?
   Answer: Yes. Power is negative when force has a component opposite to velocity, such as friction or braking force.

7. What is the SI unit of power?
   Answer: Watt.

8. Why does a car engine require more power at high speed?
   Answer: At high speed, resistive forces increase, so more power is needed to maintain or increase speed.

9. If velocity is zero, what is instantaneous power?
   Answer: Instantaneous power is zero because (P = \vec F \cdot \vec v).

10. Does a large force always mean large power?
    Answer: No. Power also depends on velocity and the angle between force and velocity.

11. If a force acts on a block but displacement is zero, is work done?
    Answer: No, work done is zero if displacement is zero.

12. If work is done slowly, what happens to power?
    Answer: Power decreases because power depends on time taken.

13. What is average power?
    Answer: Average power is total work done divided by total time taken.

14. What is linear acceleration?
    Answer: Linear acceleration is the rate of change of linear velocity with time.

15. Write the formula of linear acceleration.
    Answer: (a = \frac{dv}{dt})

16. What is the SI unit of acceleration?
    Answer: (m/s^2)

17. Can acceleration exist when speed is constant?
    Answer: Yes, if direction changes, as in circular motion.

18. Can acceleration be negative?
    Answer: Yes. Negative acceleration means acceleration is opposite to the chosen positive direction.

19. What does zero acceleration mean?
    Answer: Zero acceleration means velocity is constant.

20. If net force is zero, what is acceleration?
    Answer: Acceleration is zero according to Newton’s second law.

21. How is acceleration related to net force?
    Answer: (a = \frac{F_{net}}{m})

22. If mass increases for the same force, what happens to acceleration?
    Answer: Acceleration decreases.

23. Can a body have velocity and no acceleration?
    Answer: Yes, when it moves with constant velocity.

24. Can a body have acceleration and zero velocity at an instant?
    Answer: Yes, for example at the highest point of vertical motion.

25. Why is acceleration a vector quantity?
    Answer: Because it has both magnitude and direction.

26. What is impulse?
    Answer: Impulse is the product of force and time for which the force acts.

27. Write the formula of impulse.
    Answer: (J = F \Delta t)

28. What is impulse in terms of momentum?
    Answer: Impulse equals change in momentum: (J = \Delta p)

29. What is the SI unit of impulse?
    Answer: Newton-second or (kg,m/s).

30. Why are impulse and momentum dimensionally same?
    Answer: Because impulse equals change in momentum.

31. Why does a cricketer move hands backward while catching a ball?
    Answer: It increases the time of impact, reducing the force on hands.

32. Why are airbags used in cars?
    Answer: Airbags increase collision time, reducing impact force.

33. Why does a boxer move backward when punched?
    Answer: Moving backward increases impact time and reduces force.

34. Why does a glass break when it falls on a hard floor?
    Answer: Collision time is very small, so impact force becomes very large.

35. Why does the same glass not break easily on a soft carpet?
    Answer: Carpet increases stopping time, reducing impact force.

36. Can impulse be zero if force acts?
    Answer: Yes, if net change in momentum is zero over the interval.

37. What does area under force-time graph represent?
    Answer: It represents impulse.

38. If force is variable, how is impulse calculated?
    Answer: (J = \int F,dt)

39. Why is impulse important in collisions?
    Answer: Because collision forces act for a very short time and cause large momentum changes.

40. What is the relation between impulse and average force?
    Answer: (J = F_{avg}\Delta t)

41. A constant force acts on a body initially at rest. How does power vary with time?
    Answer: Since velocity increases linearly with time, power also increases linearly with time.

42. If force is constant, how does velocity change?
    Answer: Velocity changes linearly with time because acceleration is constant.

43. If acceleration is constant, what type of motion occurs?
    Answer: Uniformly accelerated motion occurs.

44. If power is constant and force is constant, how does velocity behave?
    Answer: Since (P = Fv), velocity remains constant if both power and force are constant.

45. If power is constant and velocity increases, what happens to force?
    Answer: Force decreases because (F = P/v).

46. Why is power not simply force multiplied by displacement?
    Answer: Force multiplied by displacement gives work, not power.

47. What happens to impulse if collision time is doubled for the same momentum change?
    Answer: Impulse remains the same, but average force becomes half.

48. Why does a bullet cause more damage than a slowly moving object of same mass?
    Answer: The bullet has much larger momentum and kinetic energy due to high velocity.

49. Can a body have high momentum but low kinetic energy?
    Answer: Yes, a very massive body moving slowly can have high momentum but relatively low kinetic energy.

50. What is the key difference between force and impulse?
    Answer: Force is an interaction at an instant, while impulse measures the total effect of force over time.