Energy & Power — 50 High-Yield MCQs (NCERT / NEET)

Covers kinetic & potential energy, work-energy theorem, power, units, conservative forces, energy conservation and quick formulas. Correct answer shown after each question.

50 MCQs
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Kinetic Energy Potential Energy Power Conservation
1. Kinetic energy of a particle of mass m and speed v is given by:
A. 1/2 m v
B. 1/2 m v^2
C. m v^2
D. m v
Answer: B
2. Potential energy near Earth's surface for mass m at height h is:
A. m g / h
B. m g h
C. m g h^2
D. 1/2 m g h
Answer: B
3. Work-energy theorem relates net work done to change in:
A. Potential energy
B. Momentum
C. Kinetic energy
D. Mechanical advantage
Answer: C
4. SI unit of energy is:
A. Watt
B. Joule
C. Newton
D. Pascal
Answer: B
5. Power is defined as the rate of doing work. Its SI unit is:
A. Joule
B. Watt (J/s)
C. N·m
D. J·s
Answer: B
6. If the speed of a particle doubles, its kinetic energy becomes:
A. Twice
B. Four times
C. Half
D. Unchanged
Answer: B
7. Potential energy of a spring compressed by x (spring constant k) is:
A. 1/2 k x
B. k x^2
C. 1/2 k x^2
D. k x
Answer: C
8. When conservative forces only act, mechanical energy (K + U) is:
A. Not conserved
B. Conserved
C. Always zero
D. Doubles
Answer: B
9. Instantaneous power delivered by force F acting on object with velocity v is:
A. F × v (cross product)
B. F · v (dot product)
C. F/v
D. v/F
Answer: B
10. Which of the following is a scalar quantity?
A. Energy
B. Force
C. Momentum
D. Acceleration
Answer: A
11. Work done by gravitational force when object moves vertically upward by h is:
A. +mgh
B. −mgh
C. Zero
D. Depends on mass only
Answer: B
12. A 10 N force moves an object with velocity 2 m/s in the direction of force. Instantaneous power is:
A. 5 W
B. 20 W
C. 12 W
D. 10 W
Answer: B
13. Work done by friction in bringing a moving object to rest equals negative of:
A. Change in potential energy
B. Initial kinetic energy
C. Total work by all forces
D. Momentum
Answer: B
14. If work done by non-conservative forces is negative, mechanical energy of system:
A. Increases
B. Decreases
C. Unchanged
D. Becomes zero
Answer: B
15. Rate of change of kinetic energy with time equals:
A. Power delivered by net force
B. Work done per displacement
C. Potential energy
D. Momentum
Answer: A
16. A body of mass m at bottom of frictionless incline with height h has potential mgh. Its speed at bottom is given by:
A. √(2gh)
B. √(gh)
C. 2gh
D. gh
Answer: A
17. Power rating of a machine is 1 kW. This means it can do work of:
A. 1000 J in 1 s
B. 100 J in 1 s
C. 1 J in 1000 s
D. 1 J in 1 s
Answer: A
18. Energy stored in a stretched spring of constant k and extension x is:
A. k x
B. 1/2 k x^2
C. k x^2
D. 1/2 k x
Answer: B
19. The kinetic energy of a system of particles about its centre of mass equals:
A. KE_total only
B. KE_cm + KE_due_to_cm_motion
C. Zero
D. Potential energy
Answer: B
20. Which of the following forces does zero work over a closed path?
A. Frictional force
B. Conservative force
C. Non-conservative force
D. Time-dependent force
Answer: B
21. Work done by gravity in lifting object slowly from Earth surface to height h equals:
A. mgh
B. −mgh
C. Zero
D. Depends on path
Answer: B
22. If energy of a system is dissipated as heat by non-conservative forces, total mechanical energy:
A. Increases
B. Decreases
C. Remains same
D. Becomes potential only
Answer: B
23. The work done by normal force when a block slides on a horizontal surface is:
A. Positive
B. Negative
C. Zero (normal perpendicular to displacement)
D. Depends on friction
Answer: C
24. Power developed when force F moves object with constant velocity v in direction of force is:
A. F/v
B. F · v
C. F + v
D. F × v
Answer: B
25. If total work done on object is zero, then change in kinetic energy is:
A. Zero
B. Positive
C. Negative
D. Depends on mass
Answer: A
26. Work done by weight when body moves along horizontal circle at constant height is:
A. Positive
B. Negative
C. Zero
D. Depends on speed
Answer: C
27. Energy required to raise a mass m from radius R to infinity in Earth's gravity is approximately:
A. GMm/R
B. GMm/2R
C. 2GMm/R
D. Zero
Answer: A
28. Efficiency of a machine is defined as:
A. Output energy / Input energy
B. Input / Output
C. Output × Input
D. Output − Input
Answer: A
29. When kinetic energy of object decreases, net work done on it is:
A. Positive
B. Negative
C. Zero
D. Infinite
Answer: B
30. Which energy is directly associated with motion of center of mass of a system?
A. Internal energy
B. Kinetic energy of CM
C. Potential energy
D. Thermal energy
Answer: B
31. Work done by variable force F(x)=ax^2 from x=0 to x=L equals:
A. a L^3 /3
B. a L^2 /2
C. a L
D. Zero
Answer: A
32. A cyclist increases speed from 5 m/s to 15 m/s. Change in kinetic energy (mass 80 kg) is approximately:
A. 8 kJ
B. 8×10^4 J
C. 8×10^2 J
D. 8 J
Answer: B
33. Work done by magnetic force on moving charge over any displacement is:
A. Positive
B. Negative
C. Zero
D. Depends on path
Answer: C
34. Work done by centripetal force over one complete circular revolution is:
A. Positive
B. Negative
C. Zero
D. Depends on speed
Answer: C
35. A body of mass m falls from rest through height h. Work done by gravity equals:
A. mgh (positive)
B. −mgh
C. Zero
D. Depends on acceleration
Answer: A
36. Average power when work W is done in time t is:
A. W × t
B. W / t
C. t / W
D. √(W t)
Answer: B
37. When a mass m with speed v strikes a wall and bounces back elastically, kinetic energy after bounce compared to before is:
A. Same
B. Double
C. Half
D. Zero
Answer: A
38. Work done by tension in string on mass moving in circle (tangential displacement) is:
A. Zero
B. Positive
C. Negative
D. Depends on mass
Answer: A
39. Energy consumed by a 60 W bulb in 2 hours is:
A. 120 Wh
B. 120 J
C. 60 Wh
D. 72000 Wh
Answer: A
40. Work done by force F parallel to displacement s equals:
A. F × s
B. F + s
C. F / s
D. Zero
Answer: A
41. If no external work is done on system, total mechanical energy is:
A. Not conserved
B. Conserved
C. Zero
D. Infinite
Answer: B
42. Work done per unit time by force on object moving with velocity v is equivalent to:
A. Power
B. Energy
C. Momentum
D. Force
Answer: A
43. Work done by conservative force between two points is path:
A. Dependent
B. Independent
C. Always zero
D. Time dependent
Answer: B
44. Work done by an external force to move a charge between two equipotential surfaces is:
A. Zero
B. qV
C. Depends on path
D. Infinite
Answer: A
45. When kinetic energy is converted into internal energy due to friction, the process is:
A. Reversible
B. Irreversible (dissipative)
C. Conservative
D. Isothermal
Answer: B
46. Power of an engine that does 5×10^6 J work in 100 s is:
A. 5×10^4 W
B. 5×10^6 W
C. 5×10^2 W
D. 5×10^1 W
Answer: A
47. A satellite in circular orbit has total mechanical energy equal to:
A. −(1/2) GMm/r
B. +(1/2) GMm/r
C. −GMm/r
D. Zero
Answer: A
48. Work done by gravitational force in moving a mass along equipotential surface is:
A. Positive
B. Negative
C. Zero
D. Depends on speed
Answer: C
49. For a conservative force, potential energy difference between two points equals negative of:
A. Work done by external agent
B. Work done by the force
C. Kinetic energy change
D. Momentum change
Answer: B
50. If a force does zero work on a particle during a displacement, then:
A. Force is zero
B. Force perpendicular to displacement
C. Displacement zero
D. Any of the above could be true
Answer: D