Question Bank – Laws of Motion

 

Question Bank – Laws of Motion

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1. Very Short Answer Questions (1 Mark)

1. State Newton’s first law of motion.

   • Answer: An object remains at rest or in uniform motion in a straight line unless acted upon by an external force.

2. What is inertia?

   • Answer: Inertia is the property of an object to resist any change in its state of motion or rest.

3. Give the SI unit of force.

   • Answer: Newton (N).

4. Define linear momentum.

   • Answer: Linear momentum is the product of the mass and velocity of an object, $p = mv$.

5. State Newton’s second law of motion.

   • Answer: The rate of change of momentum of an object is proportional to the applied force and occurs in the direction of the force.

6. What is the relationship between force and acceleration?

   • Answer: $F = ma$, where $F$ is the force, $m$ is mass, and $a$ is acceleration.

7. Define impulse.

   • Answer: Impulse is the product of force and the time for which it acts, $J = F \cdot t$.

8. What does Newton’s third law state?

   • Answer: For every action, there is an equal and opposite reaction.

9. What is the unit of momentum?

   • Answer: $\text{kg m/s}$.

10. Name the force responsible for holding a car on a curved road.

• Answer: Centripetal force.

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2. Short Answer Questions (2 Marks)

11. Why does a person fall forward when a moving bus stops suddenly?

    • Answer: Due to inertia, the upper part of the body tends to maintain its forward motion while the lower part stops with the bus.

12. State the principle of conservation of momentum.

    • Answer: The total momentum of an isolated system remains constant if no external force acts on it.

13. How is force related to the change in momentum?

    • Answer: $F = \frac{\Delta p}{\Delta t}$, where $\Delta p$ is the change in momentum.

14. Define static and kinetic friction.

    • Answer:
      • Static friction: The frictional force that opposes the relative motion when the object is at rest.
      • Kinetic friction: The frictional force acting on a moving object.

15. Why is it difficult to walk on ice?

    • Answer: Ice has a very low coefficient of friction, reducing the grip needed for walking.

16. What is the function of seat belts in cars?

    • Answer: Seat belts prevent passengers from continuing in motion (inertia) when the car stops suddenly, reducing injury.

17. Explain the term ‘pseudo force.’

    • Answer: A pseudo force is an apparent force experienced in a non-inertial frame of reference due to the acceleration of the frame.

18. Why do dust particles fall off when a carpet is beaten?

    • Answer: The carpet moves, but the dust tends to stay in place due to inertia, making it fall off.

19. What is the direction of frictional force?

    • Answer: It acts opposite to the direction of the relative motion or intended motion.

20. State two examples of Newton’s third law of motion.

    • Answer:
      • Recoil of a gun.
      • Walking, where the foot pushes the ground backward, and the ground pushes the foot forward.

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3. Numerical Problems (3 Marks)

21. Calculate the force required to accelerate a 5 kg object by 2 m/s².

    • Answer:
      $F = ma = 5 \times 2 = 10 \, N$.

22. A 20 N force is applied to a 4 kg block. Calculate its acceleration.

    • Answer:
      $a = \frac{F}{m} = \frac{20}{4} = 5 \, \text{m/s}^2$.

23. A ball of mass 0.5 kg is thrown with a velocity of 20 m/s. Calculate its momentum.

    • Answer:
      $p = mv = 0.5 \times 20 = 10 \, \text{kg m/s}$.

24. A force of 50 N acts on a body for 2 seconds. Find the impulse.

    • Answer:
      $J = F \cdot t = 50 \times 2 = 100 \, \text{Ns}$.

25. If two objects of masses 3 kg and 2 kg move towards each other with velocities 4 m/s and 5 m/s respectively, what is the total momentum?

    • Answer:
      Total momentum = $3 \times 4 - 2 \times 5 = 12 - 10 = 2 \, \text{kg m/s}$.

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4. Long Answer Questions (5 Marks)

26. State and derive the expression for Newton’s second law of motion.
27. Derive the formula for conservation of linear momentum for a system of two particles.
28. Explain the concept of friction and derive the expression for the force of friction.
29. Describe the types of friction and their properties.
30. Explain the working of a rocket based on Newton’s third law of motion.
31. Describe the role of centripetal force in circular motion.
32. Explain the concept of pseudo force with an example.
33. Why is a heavier object more difficult to accelerate? Use Newton’s second law to explain.
34. Explain why the acceleration due to gravity is independent of mass.
35. Discuss the difference between mass and weight.

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5. Higher Order Thinking Skills (HOTS) Questions

36. Why does a moving object come to rest eventually, even if no force is applied?

    • Answer: Due to friction, which opposes the motion.

37. How can a rocket move in space where there is no air?

    • Answer: The rocket expels gas backward, and the reaction force propels it forward (Newton’s third law).

38. Why does a cricket player lower his hands while catching a ball?

    • Answer: To increase the time of impact, reducing the force experienced.

39. Why does a car skid on a wet road?

    • Answer: The coefficient of friction between the tires and the road is reduced, lowering the grip.

40. How does friction affect the efficiency of a machine?

    • Answer: Friction causes energy loss in the form of heat, reducing efficiency.

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6. Assertion-Reason Type Questions

41. Assertion (A): A body moving on a frictionless surface continues to move indefinitely.
    Reason (R): There is no force to oppose its motion.

    • Answer: Both A and R are true, and R is the correct explanation.

42. Assertion (A): Static friction is greater than kinetic friction.
    Reason (R): Static friction acts when there is no relative motion.

    • Answer: Both A and R are true, and R is the correct explanation.

43. Assertion (A): Inertia depends on mass.
    Reason (R): A heavier body resists motion more than a lighter one.

    • Answer: Both A and R are true, and R is the correct explanation.

44. Assertion (A): For every action, there is an equal and opposite reaction.
    Reason (R): Newton’s third law holds for all interactions.

    • Answer: Both A and R are true, and R is the correct explanation.

45. Assertion (A): A car moving at constant speed has zero net force acting on it.
    Reason (R): The forces are balanced.

    • Answer: Both A and R are true, and R is the correct explanation.

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7. Conceptual Questions

46. How is tension in a rope affected when a block is pulled with increasing force?

    • Answer: Tension increases with the applied force.

47. Explain why a person jumping off a boat makes the boat move backward.

    • Answer: Due to conservation of momentum, the forward momentum of the person is balanced by the backward momentum of the boat.

48. Why do wet roads have lower friction?

    • Answer: Water reduces the contact between the surfaces, lowering the coefficient of friction.

49. Why does a cyclist lean inward while turning?

    • Answer: To counter the centrifugal force and maintain balance.

50. How does mass affect the momentum of an object?

    • Answer: Momentum is directly proportional to mass. A heavier object has greater momentum at the same velocity.