Covers definition of work, variable forces, work-energy theorem, work by gravity & spring, conservative forces, power and units. Correct answer shown after each question.
50 MCQs
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Work & EnergyWork-Energy TheoremConservative ForcesPower & Units
1. Work done by a constant force F on a particle displaced by displacement s is:
A. F · s (dot product)
B. |F| + |s|
C. F × s (cross product)
D. F/s
Answer: A
2. Work done by gravity when an object of mass m is lowered by height h is:
A. +mgh
B. −mgh
C. Zero
D. mgh/2
Answer: A
3. Work done by a force perpendicular to displacement is:
A. Maximum
B. Zero
C. Negative
D. Depends on magnitude
Answer: B
4. Work-energy theorem states that net work done equals change in:
A. Potential energy
B. Kinetic energy
C. Total energy
D. Momentum
Answer: B
5. Work done by friction is generally:
A. Positive
B. Zero
C. Negative (dissipative)
D. Depends on path only
Answer: C
6. Work done by spring force from x=0 to x=x0 is:
A. 1/2 k x0^2 (negative, done by spring)
B. k x0
C. Zero
D. k x0^2
Answer: A
7. If net work done on particle is zero, kinetic energy:
A. Always increases
B. Remains unchanged
C. Always decreases
D. Becomes zero
Answer: B
8. Power is defined as:
A. Work × Time
B. Work / Time
C. Force × Displacement
D. Momentum / Time
Answer: B
9. SI unit of work is:
A. Joule (N·m)
B. Watt
C. Newton
D. Pascal
Answer: A
10. Work done by gravity around a closed path is:
A. Positive
B. Negative
C. Zero
D. Depends on path
Answer: C
11. Work done in lifting mass m through height h at constant speed against gravity is:
A. mgh
B. −mgh
C. Zero
D. mg/h
Answer: A
12. Work done by normal reaction when object moves on horizontal surface is:
A. Positive
B. Negative
C. Zero (if displacement is horizontal)
D. Depends on speed
Answer: C
13. Work done by variable force F(x) from x1 to x2 is given by:
A. ∫ F(x) dx
B. dF/dx
C. F(x2) − F(x1)
D. F average × (x2 − x1)
Answer: A
14. Work done by conservative force depends on:
A. Path
B. Initial and final points only
C. Time taken
D. Speed
Answer: B
15. Potential energy function U(x) for conservative force is related by:
A. F = +dU/dx
B. F = −dU/dx
C. U = F x
D. U = ∫ F dt
Answer: B
16. Work done by force of gravity in raising a mass from Earth surface to infinity is:
A. Zero
B. +GMm/R
C. −GMm/R
D. Infinite
Answer: C
17. Work done by buoyant force when object is submerged and moved horizontally is:
A. Positive
B. Negative
C. Zero (if vertical displacement is zero)
D. Depends on density
Answer: C
18. If work done by all forces is zero, then total mechanical energy:
A. Increases
B. Decreases
C. Remains constant
D. Becomes zero
Answer: C
19. Work done by centripetal force over one complete circular orbit is:
A. Positive
B. Negative
C. Zero (force perpendicular to displacement)
D. Depends on speed
Answer: C
20. Work done by a force F when displacement is in opposite direction is:
A. Positive
B. Negative
C. Zero
D. Depends on magnitude
Answer: B
21. Instantaneous power delivered by force F moving at velocity v is:
A. F × v (cross product)
B. F · v (dot product)
C. F/v
D. v/F
Answer: B
22. Work done in compressing a spring by x is:
A. 1/2 k x^2
B. k x
C. k x^2
D. Zero
Answer: A
23. Work done by normal reaction on frictionless inclined plane as block slides down is:
A. Positive
B. Negative
C. Zero (normal perpendicular to displacement along plane)
D. Depends on angle
Answer: C
24. If force is F = k x (restoring), potential energy is:
A. 1/2 k x^2
B. k x
C. −1/2 k x^2
D. Zero
Answer: C
25. Work done by a force depends on:
A. Displacement and component of force along it
B. Magnitude of force only
C. Time only
D. Mass only
Answer: A
26. If work done by non-conservative forces is negative, mechanical energy of system:
A. Increases
B. Decreases
C. Remains same
D. Becomes zero
Answer: B
27. Average power over time interval is defined as:
A. Total work / total time
B. Instantaneous power
C. Force × average displacement
D. Energy × time
Answer: A
28. Work done by conservative force around closed loop is:
A. Path-dependent
B. Zero
C. Maximum
D. Minimum
Answer: B
29. Work done by electric conservative force between two points depends on:
A. Path
B. End points only (potential difference)
C. Time
D. Speed
Answer: B
30. Work done by weight when object moves horizontally is:
A. mgh
B. −mgh
C. Zero
D. Depends on speed
Answer: C
31. Work done by torque τ through angle θ (in radians) is:
A. τ × θ
B. τ / θ
C. τ θ^2
D. Zero
Answer: A
32. Work done by force F moving an object around a circle once when force always radial is:
A. Positive
B. Negative
C. Zero
D. Depends on speed
Answer: C
33. Work done by variable force F(x)=ax from x=0 to x=L equals:
A. a L^2 / 2
B. a L
C. a L^3 /3
D. Zero
Answer: A
34. When lifting an object at constant velocity, net work done by all forces is:
A. Positive and equals mgh
B. Zero (since KE unchanged)
C. Negative
D. Depends on mass
Answer: B
35. Work done by internal forces in a closed isolated system on the whole system is:
A. Positive
B. Negative
C. Zero (they cancel)
D. Depends on interaction
Answer: C
36. If a force does positive work on an object, the object's kinetic energy:
A. Decreases
B. Increases
C. Remains same
D. Becomes zero
Answer: B
37. Work done by force of kinetic friction over distance s is:
A. μ_k N s
B. −μ_k N s
C. Zero
D. μ_k m g
Answer: B
38. Work done by gravity moving object from r1 to r2 in central field is path:
A. Dependent
B. Independent (depends only on r1,r2)
C. Zero always
D. Infinite
Answer: B
39. Work done by force F on particle moving with displacement ds is dW =
A. F × ds
B. F · ds
C. |F|+|ds|
D. 0
Answer: B
40. Work done by a constant force of 10 N moving object 5 m in direction of force equals:
A. 2 J
B. 50 J
C. 15 J
D. 100 J
Answer: B
41. Work done by gravity to bring a mass from Earth's surface to height R (Earth radius) is approximately:
A. m g R
B. −GMm/(2R)
C. −GMm/R
D. Zero
Answer: B
42. Work done by normal force when object moves along circular path at constant height is:
A. Zero (normal perpendicular to displacement)
B. Positive
C. Negative
D. Depends on speed
Answer: A
43. Work done by tension in ideal string on mass moving in circle (string tangent) is:
A. Zero (tension radial, displacement tangential)
B. Positive
C. Negative
D. Depends on mass
Answer: A
44. If net work done equals change in kinetic energy, then work done by all forces equals:
A. ΔK
B. ΔU
C. ΔE_total
D. Zero
Answer: A
45. Work done by electric field in moving charge q between two equipotential surfaces is:
A. q × voltage difference
B. Zero (equipotential → no difference)
C. Depends on path
D. Infinite
Answer: B
46. Work done in moving small charge in uniform electric field over displacement perpendicular to field is:
A. Zero
B. q E d
C. −q E d
D. Depends on potential
Answer: A
47. Work done by magnetic force on moving charge is:
A. Positive
B. Negative
C. Zero (magnetic force perpendicular to velocity)
D. Depends on speed
Answer: C
48. Work done by force F when displacement doubles (force constant and parallel) changes by factor:
A. 1/2
B. 2
C. 4
D. Same
Answer: B
49. Work done by internal conservative forces when system moves from config A to B depends on:
A. Path
B. End configurations only
C. Time taken
D. Speed
Answer: B
50. If work done by all forces is W and change in kinetic energy is ΔK, then W =