Chapter - 4 : Questions on Laws of Motion

CLASS XI PHYSICS (THEORY)

UNIT TEST – LAWS OF MOTION

Maximum Marks: 100
Time Allowed: 3 Hours

General Instructions:

1. This question paper has five sections: A, B, C, D, and E. All sections are compulsory.
2. Section A contains 20 Multiple Choice Questions (1 mark each).
3. Section B contains 20 Assertion-Reasoning Questions (1 mark each).
4. Section C contains 20 Short Answer Questions (2 marks each).
5. Section D contains 20 Long Answer Questions (3 marks each).
6. Section E contains 20 Very Long Answer Questions with sub-parts (5 marks each).
7. There is no overall choice. Internal choice is provided in some questions.
8. Use of calculators is not allowed.

---

Section A
(Multiple Choice Questions – 1 mark each)

1. According to Newton’s first law of motion, in the absence of net external force:
   a) A body at rest remains at rest
   b) A body in motion moves with constant velocity
   c) Acceleration is zero
   d) All of the above
2. The physical quantity that measures inertia is:
   a) Velocity
   b) Acceleration
   c) Mass
   d) Force
3. The rate of change of momentum is proportional to:
   a) Velocity
   b) Acceleration
   c) Applied force
   d) Displacement
4. One newton is equivalent to:
   a) 1 kg m⁻¹ s⁻²
   b) 1 kg m s⁻²
   c) 1 kg⁻¹ m s⁻²
   d) 1 kg m² s⁻²
5. A passenger in a moving bus is thrown forward when the bus stops suddenly. This illustrates:
   a) Newton’s second law
   b) Law of inertia
   c) Conservation of momentum
   d) Impulse
6. When a bullet is fired from a gun, the gun recoils. This is due to:
   a) Conservation of kinetic energy
   b) Newton’s first law
   c) Newton’s third law
   d) Impulse
7. The force required to produce 1 m/s² acceleration in a body of mass 1 kg is:
   a) 1 dyne
   b) 1 N
   c) 10 N
   d) 100 N
8. The net force acting on a raindrop falling with constant speed is:
   a) mg downward
   b) Air resistance upward
   c) Zero
   d) mg + air resistance
9. In uniform circular motion, the centripetal force is directed:
   a) Tangentially
   b) Radially outward
   c) Radially inward
   d) Vertically downward
10. A block is at rest on a horizontal table. The normal force R and weight W are:
    a) Action-reaction pair
    b) Equal only if no other forces act
    c) Always equal and opposite
    d) Equal due to Newton’s third law
11. The coefficient of static friction is generally:
    a) Less than kinetic friction
    b) Equal to kinetic friction
    c) Greater than kinetic friction
    d) Independent of surface
12. Rolling friction is less than sliding friction because:
    a) Area of contact is less
    b) There is no relative motion at point of contact
    c) Deformation is minimal
    d) It depends on velocity
13. On a banked road, the centripetal force is provided by:
    a) Friction only
    b) Normal reaction only
    c) Horizontal component of normal reaction and friction
    d) Weight of the car
14. Impulse is equal to:
    a) Force × time
    b) Change in momentum
    c) Both (a) and (b)
    d) Acceleration
15. A stone tied to a string is whirled in a horizontal circle. If the string breaks, the stone flies:
    a) Radially outward
    b) Radially inward
    c) Tangentially
    d) Vertically downward
16. The force of gravity on a 5 kg object is:
    a) 5 N
    b) 10 N
    c) 50 N
    d) 100 N
17. In an isolated system, total momentum is:
    a) Variable
    b) Conserved
    c) Zero always
    d) Equal to kinetic energy
18. The direction of kinetic friction is:
    a) Opposite to applied force
    b) Opposite to relative motion
    c) Same as motion
    d) Perpendicular to motion
19. A ball collides with a wall and rebounds with same speed. The impulse is:
    a) Zero
    b) 2mv
    c) mv
    d) –mv
20. The force required to stop a moving body depends on:
    a) Mass and velocity
    b) Rate of change of momentum
    c) Time of stop
    d) All of the above

Section B
(Assertion and Reasoning – 1 mark each)

Directions: Choose the correct option:
a) Both A and R are true and R is the correct explanation of A.
b) Both A and R are true but R is not the correct explanation of A.
c) A is true but R is false.
d) A is false but R is true.

21. Assertion (A): A body can be at rest even when several forces act on it.
    Reason (R): Net external force must be zero for rest or uniform motion.
22. Assertion (A): Static friction is a self-adjusting force.
    Reason (R): It increases with applied force up to a limit.
23. Assertion (A): A person is thrown forward when a moving bus stops suddenly.
    Reason (R): This is due to inertia of rest.
24. Assertion (A): The centripetal force is not a new kind of force.
    Reason (R): It is always provided by real forces like tension or friction.
25. Assertion (A): Rolling friction is less than sliding friction.
    Reason (R): Rolling involves less deformation and no relative motion at contact.
26. Assertion (A): On a frictionless surface, a car cannot accelerate.
    Reason (R): Friction provides the necessary external force for motion.
27. Assertion (A): A cricketer draws hands backward while catching.
    Reason (R): This increases time and reduces force.
28. Assertion (A): The force on a body can be non-zero even if velocity is zero.
    Reason (R): Force depends on acceleration, not velocity.
29. Assertion (A): In circular motion, velocity changes even if speed is constant.
    Reason (R): Direction of velocity changes continuously.
30. Assertion (A): The force of gravity acts even when bodies are not in contact.
    Reason (R): Gravitational force is a non-contact force.
31. Assertion (A): Action and reaction act on the same body.
    Reason (R): They cancel each other.
32. Assertion (A): A horse cannot pull a cart in empty space.
    Reason (R): There is no reaction from ground in absence of friction.
33. Assertion (A): Tension in a massless string is uniform.
    Reason (R): Massless strings have infinite force constant.
34. Assertion (A): The weight of a body in a lift increases when lift accelerates upward.
    Reason (R): Normal reaction increases in this case.
35. Assertion (A): Impulse is useful in collision problems.
    Reason (R): Force and time are hard to measure separately.
36. Assertion (A): A book on a table experiences zero net force.
    Reason (R): Weight and normal force are action-reaction pair.
37. Assertion (A): A body in uniform motion does not require force to keep moving.
    Reason (R): Force is needed to overcome friction.
38. Assertion (A): The moon revolves around the earth without any engine.
    Reason (R): Gravitational force provides centripetal force.
39. Assertion (A): A cyclist leans inward while taking a turn.
    Reason (R): This provides necessary centripetal force.
40. Assertion (A): In an accelerating train, a box remains stationary due to friction.
    Reason (R): Static friction provides the same acceleration as the train.

Section C
(Short Answer Questions – 2 marks each)

41. Define inertia. Name the three types of inertia with one example each.
42. State Newton’s first law of motion. Why is it also called the law of inertia?
43. What is momentum? Give its SI unit. Is it a scalar or vector?
44. A bullet of mass 10 g moving at 200 m/s comes to rest in 0.01 s. Calculate the average force exerted.
45. Differentiate between static and kinetic friction.
46. What is impulse? Give its SI unit and one application.
47. Why are seat belts important in cars? Explain using Newton’s laws.
48. A man jumps out of a moving train. Why does he fall forward?
49. Define centripetal force. Give two examples.
50. A stone of mass 0.5 kg is tied to a string and rotated in a horizontal circle of radius 1 m at 2 m/s. Find tension.
51. Why is rolling friction less than sliding friction?
52. A block is placed on an inclined plane. At what angle does it begin to slide? Give expression.
53. State the law of conservation of momentum. Give one application.
54. What is normal reaction? Is it always equal to weight?
55. A ball rebounds from a wall with same speed. Is momentum conserved? Justify.
56. Why is it easier to pull a lawn mower than to push it?
57. A rocket is in deep space with engines off. What happens to its motion?
58. What is limiting friction? How is it related to normal reaction?
59. Explain why a horse can pull a cart on earth but not in space.
60. A car moves with constant speed on a rough road. Is net force zero? Why?

Section D
(Long Answer Questions – 3 marks each)

61. State and explain Newton’s second law of motion. Derive F = ma.
62. A body of mass 5 kg is acted upon by two perpendicular forces 12 N and 5 N. Find the magnitude and direction of acceleration.
63. Define impulse. Show that impulse equals change in momentum.
64. A car of mass 1000 kg moving at 36 km/h is brought to rest in 5 s. Calculate (i) retardation, (ii) retarding force.
65. Explain why a cricketer draws his hands backward while catching a fast ball.
66. State Newton’s third law. Give three examples from daily life.
67. Derive the expression for maximum speed of a car on a level road without skidding.
68. A block of mass 4 kg rests on a horizontal surface. Coefficient of static friction is 0.4. What minimum horizontal force is needed to move it?
69. A ball of mass 0.2 kg hits a wall with speed 10 m/s and rebounds with same speed. If contact time is 0.02 s, find average force.
70. A boy of mass 40 kg is in a lift. Find the apparent weight when lift (a) moves up with 2 m/s², (b) moves down with 2 m/s².
71. What is friction? Explain static, kinetic, and rolling friction.
72. A stone is whirled in a vertical circle. Where is tension maximum and minimum? Why?
73. A train accelerates at 2 m/s². A bob of mass 0.1 kg hangs from ceiling. Find angle with vertical.
74. A block slides down an inclined plane of angle 30°. If coefficient of kinetic friction is 0.2, find acceleration.
75. Explain the need for banking of roads. Derive expression for optimum speed.
76. Two masses 3 kg and 2 kg are connected by a string over a pulley. Find acceleration and tension.
77. A bullet of mass 0.02 kg is fired from a gun of mass 4 kg with speed 200 m/s. Find recoil speed of gun.
78. A body is in equilibrium under three concurrent forces. Show they can be represented by triangle of forces.
79. A car takes a turn of radius 50 m at 10 m/s. If μ = 0.4, will it skid? (g = 10 m/s²)
80. Explain the role of friction in walking.

Section E
(Very Long Answer Questions – 5 marks each)

81. a) State Newton’s laws of motion.
    b) Explain how Newton’s first law is a special case of the second law.
    c) A body of mass 2 kg is at rest. A force of 10 N acts for 5 s. Find final velocity.
82. a) Define momentum and impulse.
    b) Show that impulse equals change in momentum.
    c) A 0.1 kg ball moving at 15 m/s is stopped in 0.03 s. Find average force.
83. a) State the law of conservation of momentum.
    b) Derive it using Newton’s third law.
    c) A 20 g bullet is fired from a 5 kg rifle with speed 400 m/s. Find recoil velocity.
84. a) What is friction? Explain limiting friction and kinetic friction.
    b) Why is static friction called self-adjusting?
    c) A 10 kg block is on a horizontal surface (μ_s = 0.3). Find minimum force to move it.
85. a) Derive the expression for maximum speed of a car on a level road.
    b) What is the need for banking?
    c) Find optimum speed for θ = 37°, R = 100 m.
86. a) Explain the motion of a car on a banked road.
    b) Derive expression for maximum speed on a banked road with friction.
    c) Why is banking helpful?
87. a) A block of mass 5 kg is on a rough horizontal surface (μ_k = 0.2). A force of 30 N is applied horizontally. Find acceleration.
    b) What would be acceleration if force is removed?
88. a) Draw free-body diagrams of a block on an inclined plane.
    b) Derive expression for acceleration down the plane.
    c) At what angle does it begin to slide if μ_s = 0.5?
89. a) Explain why a cyclist leans while taking a turn.
    b) Derive expression for angle of banking.
    c) A cyclist takes turn of radius 20 m at 10 m/s. Find angle.
90. a) A man of mass 60 kg stands on a weighing machine in a lift.
    b) Find reading when lift (i) moves up with 3 m/s², (ii) moves down with 3 m/s², (iii) falls freely.
    c) Why is weight zero in free fall?
91. a) Two masses 6 kg and 4 kg are connected by a string over a frictionless pulley.
    b) Find acceleration and tension.
    c) What happens if masses are equal?
92. a) A stone of mass 0.2 kg is tied to a 1 m string. Maximum tension is 100 N.
    b) Find maximum speed in horizontal circle.
    c) What happens if speed exceeds this?
93. a) What is rolling friction? Why is it less than sliding friction?
    b) How can friction be reduced in machines?
    c) Give two advantages of friction.
94. a) Explain the concept of action and reaction with examples.
    b) Why can’t action and reaction cancel each other?
    c) A bird flies in a cage. Does the cage’s weight change?
95. a) A ball of mass 0.15 kg hits a wall at 12 m/s and rebounds at 10 m/s. Contact time = 0.01 s.
    b) Find impulse and average force.
    c) Is momentum conserved?
96. a) A car of mass 1200 kg takes a turn of radius 40 m. Coefficient of friction = 0.5.
    b) Find maximum safe speed.
    c) What happens if speed exceeds this?
97. a) Define free-body diagram. Why is it important?
    b) Draw FBD of a block on a horizontal surface with applied force.
    c) How does it help in solving mechanics problems?
98. a) A rocket of mass 5000 kg blasts off with acceleration 6 m/s².
    b) Find thrust (g = 10 m/s²).
    c) Why is thrust greater than weight?
99. a) A bob of mass 0.2 kg is oscillating. String is cut at extreme and mean positions.
    b) Describe the path in each case.
    c) Why does the path differ?
100. a) A 3 kg block is pulled by 20 N on a surface (μ_k = 0.1).
     b) Find acceleration.
     c) What force is needed to move it with constant velocity?

---

Answer Key & Marking Scheme

Section A (1×20 = 20 marks)

1. d
2. c
3. c
4. b
5. b
6. c
7. b
8. c
9. c
10. b
11. c
12. b
13. c
14. c
15. c
16. c
17. b
18. b
19. b
20. d

Section B (1×20 = 20 marks)

21. a
22. a
23. c
24. a
25. a
26. a
27. a
28. a
29. a
30. a
31. d
32. a
33. b
34. a
35. a
36. c
37. a
38. a
39. a
40. a

Section C (2×20 = 40 marks)

41. Inertia: Resistance to change in state. Types: (1) Rest (person falls back), (2) Motion (thrown forward), (3) Direction (mud flies tangentially).
42. First law: Body remains at rest/uniform motion unless acted upon by net external force. Called law of inertia because it defines inertia.
43. Momentum = mv. SI unit: kg m/s. It is a vector.
44. a = (0 – 200)/0.01 = –20000 m/s², F = ma = 0.01 × 20000 = 200 N.
45. Static friction: opposes impending motion; kinetic friction: opposes actual motion. μ_s > μ_k.
46. Impulse = FΔt = Δp. Unit: Ns. Application: cricketer catching.
47. Prevents forward motion due to inertia when car stops suddenly. Newton’s first law.
48. Due to inertia of motion, body continues forward.
49. Centripetal force: Force toward center. Examples: tension, friction.
50. T = mv²/r = 0.5×4/1 = 2 N.
51. No relative motion at contact point; less deformation ⇒ less friction.
52. At angle of repose, tanθ = μ_s.
53. Total momentum conserved in isolated system. Application: rocket propulsion.
54. Normal reaction: Perpendicular contact force. Equal to weight only if no vertical acceleration.
55. No for ball alone; yes for system (ball + wall).
56. Pulling reduces normal force ⇒ reduces friction. Pushing increases it.
57. Moves with constant velocity (Newton’s first law).
58. Limiting friction: Maximum static friction. f_max = μ_s N.
59. Horse pushes ground; ground pushes horse forward (action-reaction). No ground in space.
60. Yes, net force zero ⇒ acceleration zero.

Section D (3×20 = 60 marks)

61. Second law: Rate of change of momentum ∝ applied force. F = dp/dt = m dv/dt = ma. So F = ma.
62. F_net = √(12²+5²) = 13 N, a = F/m = 13/5 = 2.6 m/s², direction: tan⁻¹(5/12) ≈ 22.6°.
63. Impulse = FΔt. From F = Δp/Δt ⇒ FΔt = Δp ⇒ impulse = change in momentum.
64. u = 10 m/s, t = 5 s, a = –2 m/s², F = 1000×(–2) = –2000 N.
65. Increases time ⇒ reduces force (F = Δp/Δt). Prevents injury.
66. Third law: Every action has equal and opposite reaction. Examples: walking, rocket, book on table.
67. F_c = f ⇒ mv²/R = μ_s mg ⇒ v_max = √(μ_s R g).
68. f_max = μ_s N = 0.4 × 40 = 16 N.
69. Δp = –0.2×10 – (0.2×10) = –4 kg m/s, F_avg = –4/0.02 = –200 N.
70. (a) R = m(g+a) = 40×12 = 480 N; (b) R = m(g–a) = 40×8 = 320 N.
71. Friction: Opposes relative motion. Static: no motion; kinetic: sliding; rolling: least.
72. Max tension at bottom (T = mg + mv²/r), min at top (T = mv²/r – mg).
73. tanθ = a/g = 2/10 = 0.2 ⇒ θ ≈ 11.3°.
74. a = g(sinθ – μ_k cosθ) = 10(0.5 – 0.2×0.866) ≈ 3.27 m/s².
75. Reduces dependence on friction. v₀ = √(Rg tanθ).
76. a = (m₁–m₂)g/(m₁+m₂) = 2 m/s², T = 2m₁m₂g/(m₁+m₂) = 24 N.
77. m₁v₁ = m₂v₂ ⇒ 0.02×200 = 4×v ⇒ v = 1 m/s.
78. For equilibrium, vector sum = 0 ⇒ forces form closed triangle.
79. v_max = √(0.4×50×10) ≈ 14.14 m/s. Since 10 < 14.14, no skid.
80. Foot pushes ground backward; ground pushes forward ⇒ motion.

Section E (5×20 = 100 marks)

(Each answer carries 5 marks – split as per sub-parts)

81. a) State all 3 laws (1) b) F=0 ⇒ a=0 ⇒ uniform motion (2) c) v = u + at = 0 + 10×5/2 = 25 m/s (2)
82. a) Definitions (2) b) FΔt = Δp (2) c) F = Δp/Δt = (0 – 1.5)/0.03 = –50 N (1)
83. a) Statement (1) b) F₁₂ = –F₂₁ ⇒ Δp₁ = –Δp₂ ⇒ Δp_total = 0 (2) c) v = (0.02×400)/5 = 1.6 m/s (2)
84. a) Definitions (2) b) Adjusts up to μ_sN (1) c) F_min = 0.3×100 = 30 N (2)
85. a) v_max = √(μRg) (2) b) Reduces wear, allows higher speed (1) c) v₀ = √(100×10×tan37°) ≈ 27.4 m/s (2)
86. a) N and f provide centripetal force (1) b) v_max = √[Rg(tanθ + μ)/(1 – μ tanθ)] (3) c) Reduces friction need (1)
87. a) f_k = 10 N, F_net = 20 N, a = 4 m/s² (3) b) a = –2 m/s² (2)
88. a) FBD with mg, N, f (1) b) a = g(sinθ – μ_k cosθ) (2) c) θ = tan⁻¹(0.5) ≈ 26.6° (2)
89. a) To provide centripetal component (1) b) tanθ = v²/(Rg) (2) c) θ = tan⁻¹(0.5) ≈ 26.6° (2)
90. a) Concept (1) b) (i) 780 N, (ii) 420 N, (iii) 0 N (3) c) No normal force (1)
91. a) a = 2 m/s² (2) b) T = 48 N (2) c) a = 0, T = mg (1)
92. a) v = √(Tr/m) = √(100×1/0.2) = √500 ≈ 22.36 m/s (3) b) Flies tangentially (2)
93. a) Minimal relative motion ⇒ less friction (2) b) Ball bearings, lubricants (2) c) Walking, braking (1)
94. a) Examples: rocket, walking (2) b) Act on different bodies (2) c) Weight same (1)
95. a) Δp = –3.3 Ns (2) b) F = –330 N (2) c) Only if wall included (1)
96. a) v_max = √(0.5×40×10) = √200 ≈ 14.14 m/s (3) b) Skids outward (2)
97. a) Diagram showing all forces (2) b) FBD with mg, N, F, f (2) c) Isolates system (1)
98. a) F_thrust – mg = ma (2) b) F = 5000×16 = 80,000 N (2) c) To accelerate upward (1)
99. a) Falls vertically (1) b) Projectile motion (2) c) At extreme: v=0; at mean: v≠0 (2)
100. a) a = 17/3 ≈ 5.67 m/s² (3) b) F = 3 N (2)

Prepared by: CBSE Physics Examiner | Based on NCERT Class XI – Chapter 4: Laws of Motion

All the best for your AISSCE 2026 preparation!