#Question 1 of 20Score: +1.0 / -0.25
Work, Power, Kinetic and Potential Energy
Practice work-power-and-energy with 20 free MCQ questions covering general-physics. Detailed explanations in English and Hindi, perfect for UPSC, SSC, and competitive exam preparation.
FreePrep.inWork, Power, Kinetic and Potential Energy20:00
Work, Power, Kinetic and Potential Energy20:00
work-power-and-energy — Answer Key & Explanations (20 Questions)
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Attempt the quiz above first, then review every question with its correct answer and a short explanation below.
Q1.The SI unit of work is:
- A.joule✓ Correct Answer
- B.watt
- C.newton
- D.pascal
Explanation: Work = force × displacement, measured in joules.
Q2.The kinetic energy of a body of mass m moving with speed v is:
- A.½mv²✓ Correct Answer
- B.mv
- C.mv²
- D.mgh
Explanation: Kinetic energy grows with the square of speed.
Q3.Work done by a force is zero when the force is:
- A.along the displacement
- B.opposite to the displacement
- C.perpendicular to the displacement✓ Correct Answer
- D.very large
Explanation: W = Fs cos 90° = 0.
Q4.A stretched spring possesses:
- A.kinetic energy only
- B.heat energy only
- C.no energy
- D.potential energy✓ Correct Answer
Explanation: Work done in stretching is stored as elastic potential energy.
Q5.One kilowatt-hour is equal to:
- A.3.6 × 10^3 joules
- B.3.6 × 10^6 joules✓ Correct Answer
- C.1,000 joules
- D.746 joules
Explanation: 1 kW × 3,600 s = 3.6 million joules.
Q6.The commercial unit of electrical energy is:
- A.kilowatt-hour✓ Correct Answer
- B.watt
- C.joule
- D.ampere
Explanation: Electricity bills are in kilowatt-hours, called units.
Q7.The gravitational potential energy of a mass m at height h is:
- A.½mgh
- B.mg/h
- C.mh/g
- D.mgh✓ Correct Answer
Explanation: Potential energy grows linearly with height.
Q8.The law of conservation of energy states that energy:
- A.can be created
- B.can be destroyed
- C.always increases
- D.can neither be created nor destroyed, only transformed✓ Correct Answer
Explanation: The total energy of an isolated system is constant.
Q9.The kinetic energy of a 2 kg body moving at 3 m/s is:
- A.3 J
- B.6 J
- C.9 J✓ Correct Answer
- D.18 J
Explanation: ½ × 2 × 9 = 9 J.
Q10.If the velocity of a body is doubled, its kinetic energy becomes:
- A.two times
- B.half
- C.unchanged
- D.four times✓ Correct Answer
Explanation: Kinetic energy is proportional to v².
Q11.Power is defined as:
- A.work done per unit time✓ Correct Answer
- B.force per unit area
- C.energy per unit mass
- D.work per unit length
Explanation: P = W/t, in watts.
Q12.A person walks carrying a load horizontally. The work done against gravity is:
- A.equal to mgh
- B.zero✓ Correct Answer
- C.equal to mg
- D.positive and large
Explanation: The force of support is perpendicular to the displacement.
Q13.During free fall from a height h, at the mid-point the kinetic energy equals:
- A.twice the potential energy
- B.zero
- C.the potential energy✓ Correct Answer
- D.four times the potential energy
Explanation: Half the initial potential energy has converted to kinetic energy.
Q14.A dynamo converts:
- A.electrical energy into mechanical energy
- B.mechanical energy into electrical energy✓ Correct Answer
- C.heat into light
- D.chemical energy into sound
Explanation: An electric motor does the reverse.
Q15.The efficiency of any real machine is always:
- A.equal to 100 per cent
- B.less than 100 per cent✓ Correct Answer
- C.more than 100 per cent
- D.exactly 50 per cent
Explanation: Some energy is always lost to friction and heat.
Q16.The work done in lifting a 5 kg mass through 2 m (take g = 10 m/s²) is:
- A.100 J✓ Correct Answer
- B.10 J
- C.50 J
- D.25 J
Explanation: W = mgh = 5 × 10 × 2.
Q17.A pump lifts 100 kg of water through 10 m in 10 s (g = 10 m/s²). Its power output is:
- A.100 W
- B.10,000 W
- C.1,000 W✓ Correct Answer
- D.10 W
Explanation: Work = 100 × 10 × 10 = 10,000 J, over 10 s.
Q18.The kinetic energy of a body in terms of its momentum p and mass m is:
- A.2p²/m
- B.pm/2
- C.p/2m
- D.p²/2m✓ Correct Answer
Explanation: Substituting v = p/m in ½mv².
Q19.According to the work-energy theorem, the net work done on a body equals the change in its:
- A.potential energy
- B.kinetic energy✓ Correct Answer
- C.momentum
- D.mass
Explanation: W = ΔKE.
Q20.Two bodies of different masses have equal momentum. The lighter body has:
- A.smaller kinetic energy
- B.equal kinetic energy
- C.greater kinetic energy✓ Correct Answer
- D.zero kinetic energy
Explanation: KE = p²/2m, so smaller mass means larger KE.