Laws of Motion — 50 High-Yield MCQs (NCERT / NEET)

Focused on Newton's laws, friction, impulse, momentum, Atwood systems, pulley & constraint problems. Correct answer is shown after each question.

50 MCQs
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Newton I, II, III Friction Impulse & Momentum Pulleys & Atwood
1. Which law states that net force equals rate of change of momentum?
A. Newton's First Law
B. Newton's Second Law
C. Newton's Third Law
D. Law of Conservation of Energy
Answer: B
2. For a body of constant mass, F = ma follows from which expression?
A. F = m dv/dt
B. F = d(mv)/dt
C. Both A and B
D. Neither
Answer: C
3. Two bodies exert forces on each other. The forces are equal and opposite. This is statement of:
A. Newton's First Law
B. Newton's Second Law
C. Newton's Third Law
D. Conservation of Momentum
Answer: C
4. A block on a rough horizontal table is pushed with constant horizontal force and moves at constant velocity. The frictional force equals:
A. Greater than applied force
B. Less than applied force
C. Equal to applied force
D. Zero
Answer: C
5. Maximum static friction depends on:
A. Area of contact
B. Relative speed
C. Normal reaction
D. Time of contact
Answer: C
6. A car negotiates a flat curve at constant speed. What causes centripetal acceleration?
A. Tangential friction
B. Centripetal friction (lateral friction)
C. Engine force
D. Gravity
Answer: B
7. A 2 kg body experiences impulse of 10 N·s. Change in its velocity is:
A. 2 m/s
B. 5 m/s
C. 10 m/s
D. 20 m/s
Answer: B
8. In an elastic head-on collision between equal masses where one is stationary, after collision:
A. Both move together
B. Incoming passes through
C. The incoming stops and target moves with incoming speed
D. Both reverse direction
Answer: C
9. For Atwood machine with masses m1 and m2 (m2>m1), acceleration of heavier mass is:
A. (m2-m1)g/(m1+m2)
B. (m1+m2)g/(m2-m1)
C. (m1-m2)g/(m1+m2)
D. g(m1 m2)
Answer: A
10. A puck slides without friction on ice. Which quantity remains constant?
A. Speed
B. Velocity
C. Momentum
D. Kinetic friction
Answer: C
11. A 5 kg body is pulled horizontally with 20 N. Frictional force is 8 N. Acceleration is:
A. 4 m/s²
B. 2.4 m/s²
C. 12 m/s²
D. 0 m/s²
Answer: B
12. A block on incline (angle θ) will start sliding when:
A. μ_s > tanθ
B. μ_s = tanθ
C. μ_s < tanθ
D. μ_k > tanθ
Answer: C
13. A force acting perpendicular to velocity does what to speed?
A. Increases speed
B. Decreases speed
C. Does not change speed
D. Reverses speed
Answer: C
14. A particle moves in circle at constant speed v. Magnitude of centripetal force is:
A. m v / r
B. m v^2 / r
C. m r ω
D. m ω / r
Answer: B
15. If net external force on system = 0, then:
A. Total momentum constant
B. Total kinetic energy constant
C. Centre of mass at rest
D. All internal forces zero
Answer: A
16. A force acts for short time Δt causing change in momentum Δp. Average force is:
A. Δp / Δt
B. Δt / Δp
C. Δp × Δt
D. Δp
Answer: A
17. Pseudo force in non-inertial accelerating frame equals:
A. m a_frame (same direction)
B. −m a_frame (opposite direction)
C. Zero
D. m g
Answer: B
18. Two masses connected by light string on horizontal table; one mass is pulled with constant force, string remains taut. Tension equals:
A. Same as pull force
B. Force divided by number of masses (in series)
C. Zero
D. Equal to friction
Answer: B
19. A bomb at rest explodes into fragments. Total momentum after explosion is:
A. Zero
B. Non-zero
C. Depends on mass
D. Depends on energy released
Answer: A
20. A box is pulled with force F at angle θ above horizontal. Normal reaction is:
A. mg
B. mg + F sinθ
C. mg − F sinθ
D. mg + F cosθ
Answer: C
21. A body of mass m experiences three forces that sum to zero. Its acceleration is:
A. Zero
B. g
C. Depends on individual forces
D. Infinity
Answer: A
22. Coefficient of restitution e = 0 corresponds to:
A. Perfectly elastic collision
B. Perfectly inelastic collision (objects stick)
C. No collision
D. Elastic and inelastic mix
Answer: B
23. For a body sliding with kinetic friction f_k = μ_k N, work done by friction over displacement s equals:
A. μ_k N s
B. −μ_k N s
C. Zero
D. μ_k m g
Answer: B
24. A particle of mass m attached to string rotates horizontally. Required tension T for circular motion of radius r with speed v is:
A. m v / r
B. m v^2 / r
C. m r v^2
D. m v^2 r
Answer: B
25. In a moving train accelerating forward, a hanging bob deflects. The deflecting pseudo-force is:
A. Forward
B. Backward
C. Upward
D. Downward
Answer: B
26. A raindrop falls with constant velocity. Net force on it is:
A. Downwards mg
B. Upwards due to air resistance
C. Zero
D. Depends on size
Answer: C
27. A body of mass m is pulled by two equal and opposite forces. Net force is:
A. 2F
B. F
C. Zero
D. Depends on angle
Answer: C
28. For a massless frictionless pulley, tension is:
A. Same on both sides
B. Different on sides
C. Zero
D. Depends on mass
Answer: A
29. A block of mass m has acceleration a when pulled by force F on rough surface. If mass doubled and same F applied, acceleration becomes:
A. a/2
B. 2a
C. a
D. 0
Answer: A
30. A bullet of mass m hits and sticks to block of mass M. Momentum conservation implies final velocity v =
A. m/(M+m) × initial velocity
B. (m+M)/m × initial
C. m×M / (m+M)
D. initial velocity
Answer: A
31. A 10 N force acts on 2 kg mass for 0.5 s. Change in momentum equals:
A. 5 N·s
B. 20 N·s
C. 10 N·s
D. 2.5 N·s
Answer: A
32. Two equal and opposite forces act on a body but at different points. The net force and net torque are respectively:
A. Zero and zero
B. Zero and non-zero (couple)
C. Non-zero and zero
D. Non-zero and non-zero
Answer: B
33. For a body in equilibrium, sum of forces and sum of moments about any point are:
A. Zero and zero
B. Zero and non-zero
C. Non-zero and zero
D. Both non-zero
Answer: A
34. A particle experiences acceleration proportional to displacement (a = −ω^2 x). This motion is:
A. Uniform acceleration
B. Simple harmonic motion
C. Exponential growth
D. Random
Answer: B
35. A body is moving under action of only conservative forces. Total mechanical energy:
A. Increases
B. Decreases
C. Remains constant
D. Becomes zero
Answer: C
36. A mass m is attached to ceiling by two strings making angles 30° and 60°. Tensions generally are:
A. Equal
B. Different, found by vertical equilibrium
C. Zero
D. Infinite
Answer: B
37. A car brakes to stop; force of braking does negative work. Kinetic energy change equals:
A. Work done by braking (negative)
B. Zero
C. Positive value equal to work
D. Depends on mass
Answer: A
38. If external torque about CM is zero, angular momentum about CM is:
A. Conserved
B. Zero
C. Changes linearly
D. Depends on mass
Answer: A
39. A block of mass m on horizontal table connected to hanging mass M over pulley moves. If M>m, direction of motion is:
A. Block moves toward pulley
B. Block moves away from pulley
C. Remains at rest
D. Depends on friction
Answer: A
40. A force F applied for very short time produces large impulse. Which is true?
A. Δp small
B. Δp large
C. Energy conserved
D. Momentum not affected
Answer: B
41. A mass m moves with acceleration a horizontally; work done by net force in displacement s is:
A. m a s
B. 1/2 m v^2
C. m v
D. Zero
Answer: A
42. A particle moves under constant force; acceleration is:
A. Constant
B. Variable
C. Zero
D. Infinite
Answer: A
43. If two bodies are connected by inextensible string, their accelerations are:
A. Independent
B. Related by constraint
C. Equal always
D. Opposite signs always
Answer: B
44. Momentum flux concept applies to:
A. Solid mechanics only
B. Fluid flow and collisions
C. Thermodynamics
D. Optics
Answer: B
45. When a body moves under two perpendicular forces of equal magnitude, the resultant acceleration direction is:
A. Along one of forces
B. At 45° to them
C. Opposite
D. Random
Answer: B
46. A body attached to spring oscillates; net restoring force is proportional to:
A. Velocity
B. Displacement
C. Time
D. Square of displacement
Answer: B
47. A mass sliding down frictionless incline converts potential energy to:
A. Heat
B. Kinetic energy
C. Sound
D. None
Answer: B
48. If net torque about an axis is zero, rotational speed about that axis:
A. Increases
B. Decreases
C. Remains constant
D. Becomes zero
Answer: C
49. A child jumps off a stationary cart; cart moves backward due to:
A. External force
B. Conservation of momentum (internal forces)
C. Gravity only
D. Friction only
Answer: B
50. A mass m moves under net force F; if F doubles, acceleration:
A. Halves
B. Doubles
C. Unchanged
D. Squares
Answer: B