Class 9th Science Force and Laws of Motion Practice Questions

Section A – Multiple Choice Questions (MCQs) [Q.1–20]

(No figures in this section)

1. The SI unit of force is:
   a) Joule
   b) Newton
   c) Dyne
   d) Pascal
2. A body continues in its state of rest or uniform motion unless acted upon by an external force. This is:
   a) Newton’s 1st law
   b) Newton’s 2nd law
   c) Newton’s 3rd law
   d) Law of gravitation
3. Force = mass × __________.
   a) Time
   b) Acceleration
   c) Velocity
   d) Momentum
4. Which of the following is a vector quantity?
   a) Mass
   b) Force
   c) Speed
   d) Distance
5. The inertia of a body depends on its:
   a) Velocity
   b) Mass
   c) Acceleration
   d) Shape
6. Rate of change of momentum is equal to:
   a) Acceleration
   b) Force
   c) Impulse
   d) Inertia
7. Momentum is defined as:
   a) Force × distance
   b) Mass × velocity
   c) Mass × acceleration
   d) Mass ÷ velocity
8. A goalkeeper pulls back his hands while catching a fast-moving ball. This is to:
   a) Increase mass
   b) Decrease impulse
   c) Increase time of impact
   d) Stop momentum
9. Action and reaction:
   a) Act on same body
   b) Act on different bodies
   c) Cancel each other
   d) None of these
10. A horse pulls a cart. The cart moves forward because:
    a) Horse pushes against air
    b) Cart pushes horse forward
    c) Horse pushes ground backward
    d) None of these
11. If the net external force on a body is zero, its momentum:
    a) Increases
    b) Decreases
    c) Remains constant
    d) Becomes zero
12. The law of conservation of momentum is a consequence of:
    a) Newton’s first law
    b) Newton’s second law
    c) Newton’s third law
    d) Law of inertia
13. A passenger jumps out of a moving bus. He falls forward because of:
    a) Momentum of body
    b) Inertia of rest
    c) Inertia of motion
    d) Acceleration
14. Rocket propulsion works on:
    a) Newton’s first law
    b) Newton’s second law
    c) Newton’s third law
    d) Gravitation
15. The unit of momentum is:
    a) kg·m/s
    b) N·m
    c) J
    d) N/s
16. A bullet of mass 10 g moving with 400 m/s has momentum:
    a) 0.4 Ns
    b) 40 Ns
    c) 4 Ns
    d) 0.04 Ns
17. The SI unit of impulse is same as that of:
    a) Force
    b) Energy
    c) Momentum
    d) Work
18. A body moving with uniform velocity:
    a) Has no acceleration
    b) Has constant acceleration
    c) Has variable acceleration
    d) Has negative acceleration
19. The inertia of direction is seen when:
    a) A coin falls when cardboard is pulled
    b) A passenger falls forward in bus
    c) A passenger is thrown sideways on turning
    d) None of these
20. A body of mass 5 kg moving with 2 m/s has momentum:
    a) 2 kg·m/s
    b) 10 kg·m/s
    c) 5 kg·m/s
    d) 20 kg·m/s

Section B – True/False [Q.21–30]

21. Newton’s first law is called law of inertia.
22. A heavier body has less inertia.
23. Action and reaction act on same body.
24. Momentum is a scalar quantity.
25. Force is directly proportional to acceleration.
26. Momentum is conserved in all types of collisions.
27. Rocket propulsion is based on conservation of momentum.
28. Inertia is independent of mass.
29. If net force = 0, velocity remains constant.
30. Impulse = Force × Time.

Section C – Fill in the Blanks [Q.31–40]

31. The tendency of a body to resist change in its state is called __________.
32. The product of mass and velocity is __________.
33. For every action, there is an __________ and __________ reaction.
34. The SI unit of momentum is __________.
35. Impulse is equal to change in __________.
36. The rate of change of momentum is directly proportional to __________.
37. A passenger falls forward in a moving bus when it stops suddenly due to __________.
38. The law of conservation of momentum follows from Newton’s __________ law.
39. Momentum is a __________ quantity.
40. A rocket moves forward by expelling gases __________.

Section D – Assertion & Reason [Q.41–50]

41. Assertion (A): A person in a car jerks backward when the car suddenly moves forward.
Reason (R): Due to inertia of rest, the body resists the change in its state.

42. Assertion (A): A ball thrown vertically upwards comes down after reaching a certain height.
Reason (R): The Earth exerts an unbalanced force of gravity on the ball.

43. Assertion (A): The recoil velocity of a gun is much smaller than the velocity of the bullet.
Reason (R): The gun has a much larger mass compared to the bullet.

Q44.
Assertion (A): A man cannot lift himself by pulling up the straps of his shoes.
Reason (R): Action and reaction forces act on different bodies.

45. Assertion (A): Momentum is conserved when two bodies collide in the absence of external force.
Reason (R): The force exerted by one body on the other is equal and opposite to the reaction force.

46 .Assertion (A): A passenger falls forward when the bus suddenly stops.
Reason (R): Due to inertia of motion, the upper part of the body continues to move forward.

47. Assertion (A): A horse is able to pull a cart and make it move forward.
Reason (R): The horse pushes the ground backward, and the ground pushes the horse forward.

48. Assertion (A): Newton’s Second Law of Motion gives a quantitative definition of force.
Reason (R): It relates force with the rate of change of momentum.

49. Assertion (A): If no force acts on a moving body, it will continue moving with uniform velocity.
Reason (R): Inertia opposes any change in the state of motion of a body.

50.Assertion (A): In action–reaction pair, action and reaction do not cancel each other.
Reason (R): They act on two different bodies.

Section E – Very Short Answer (1 Mark Each) [Q.51–60]

51. Define inertia.
52. Write SI unit of force.
53. State Newton’s 1st law of motion.
54. Define momentum.
55. State Newton’s 3rd law.
56. Give an example of inertia of rest.
57. Write mathematical form of 2nd law.
58. Define impulse.
59. State law of conservation of momentum.
60. Give an example of action–reaction pair.

Section F – Short Answer (2 Marks Each) [Q.61–70]

61. Why does a cyclist fall sideways when taking a sharp turn?
62. Explain why passengers fall backward when bus starts suddenly.
63. Derive relation between impulse and momentum.
64. Why is it easier to stop a tennis ball than a cricket ball moving with same velocity?
65. A body of mass 50 kg is moving with velocity 10 m/s. Calculate its momentum.
66. State two applications of Newton’s 3rd law.
67. Why does a rifle recoil backward?
68. How does seat belt protect passengers in car accidents?
69. A hammer strikes a nail. Explain action and reaction here.
70. Why does a balloon move forward when air is released?

Section G – Short Answer (3 Marks Each) [Q.71–80]

71. Derive F = ma from Newton’s second law.
72. Explain conservation of momentum with an example.
73. Why does a cricket player lower his hands while catching a ball?
74. A bullet of mass 20 g is fired with velocity 200 m/s from gun of mass 10 kg. Find recoil velocity of gun.
75. A boy of mass 40 kg jumps from 5 m height. What is his momentum just before hitting ground?
76. A truck of mass 3000 kg moving with 72 km/h collides with car of mass 1000 kg at rest. They move together. Find common velocity.
77. Derive relation between force and rate of change of momentum.
78. Why is it difficult to walk on ice?
79. Why does a person fall backwards when pushing a wall?
80. Define second law of motion.

Section H – Long Answer (4–5 Marks Each, with Figures) [Q.81–90]

81. State and explain Newton’s three laws with suitable daily life examples.
82. Derive mathematical form of Newton’s 2nd law using momentum.
83. A ball of mass 200 g moving at 10 m/s strikes wall at 90° and rebounds with same speed. Find change in momentum.
84. A truck of mass 2000 kg moving at 36 km/h is stopped by force 2000 N. Find stopping distance.
85. Why are road accidents less severe at lower speeds? Explain with laws of motion.
86. A car of mass 1000 kg moving at 20 m/s is stopped by brakes in 5 s. Calculate force.
87. A truck of mass 3000 kg moving with a velocity of 90 km/h collides with a car of mass 1000 kg moving with a velocity of 18 km/h in the same direction. After collision, both move together. Calculate their common velocity after collision. Also explain which principle is used in solving this problem.
88. Explain why a cricket player lowers his hands while catching a fast-moving ball. Derive the mathematical form of Newton’s Second Law of Motion and show how Force = mass × acceleration.
89. Describe the working of a rocket on the basis of Newton’s Third Law of Motion. With the help of equations of motion, derive the expression for conservation of momentum in a system of two bodies interacting with each other.
90. State and explain Newton’s three laws of motion with suitable daily-life examples. Draw neat diagrams wherever necessary.

Section I – Case Study Based [Q.91–100]

Case 1 – Colliding Carts

Two carts of masses 2 kg and 3 kg collide. The first moving at 4 m/s comes to rest, second moves away.

91. Which law applies here?
92. State law of conservation of momentum.
93. Calculate velocity of 3 kg cart after collision.
94. What type of collision is this?
95. Draw momentum-time graph.

Case 2 – Rocket Motion

A rocket expels gases at high velocity.

96. Which Newton’s law explains it?
97. If rocket expels 10 kg gases/s at 500 m/s, what thrust is produced?
98. Why does rocket accelerate upwards?
99. Explain how momentum is conserved in rocket propulsion.
100. What is action and reaction force?