30 multiple-choice questions on the topic "Work, Energy and Power" for Class 12 students with answers and brief explanations:
Work is done when:
a) There is force but no displacement
b) There is displacement but no force
c) Force and displacement are perpendicular
d) A force causes displacement in its direction
Answer: d) A force causes displacement in its direction
Explanation: Work requires force and displacement in the same direction or with an angle.
If the velocity of a body is doubled, its kinetic energy becomes:
a) Double
b) Four times
c) Half
d) Same
Answer: b) Four times
Explanation: Kinetic energy KE=1/2mv2 ; doubling velocity quadruples KE.
The SI unit of power is:
a) Joule
b) Watt
c) Newton
d) Coulomb
Answer: b) Watt
Explanation: Power is work done per unit time, measured in watts.
A 1 kg stone is raised to a height of 10 m (g=10 m/s²). The potential energy gained is:
a) 100 J
b) 10 J
c) 1000 J
d) 1 J
Answer: a) 100 J
Explanation: PE=mgh=1×10×10=100 J
Work done by gravity when lifting a ball upwards is:
a) Positive
b) Negative
c) Zero
d) Infinite
Answer: b) Negative
Explanation: Gravity does negative work as it opposes displacement direction.
Kinetic energy of a 50 kg body moving at 2 m/s is:
a) 100 J
b) 200 J
c) 150 J
d) 80 J
Answer: a) 100 J
Explanation: KE=12×50×2^2=100 J
When an object reaches the highest point of its motion, its energy is mostly:
a) Kinetic energy
b) Potential energy
c) Thermal energy
d) Electrical energy
Answer: b) Potential energy
Explanation: At maximum height, velocity is zero and energy is potential.
Work done is maximum when the angle between force and displacement is:
a) 0°
b) 45°
c) 90°
d) 180°
Answer: a) 0°
Explanation: Work done = Fd cos θ, maximum when θ=0∘.
Total mechanical energy of a system is:
a) Potential energy only
b) Kinetic energy only
c) Sum of kinetic and potential energy
d) Zero
Answer: c) Sum of kinetic and potential energy
Explanation: Mechanical energy is conserved and equals sum of KE and PE.
Power is defined as:
a) Work done × time
b) Work done / time
c) Force × displacement
d) Force / velocity
Answer: b) Work done / time
Explanation: Power indicates the rate of doing work.
Electric potential difference of 1.5 V moves 60 coulombs charge. The energy transferred is:
a) 40 J
b) 90 J
c) 60 J
d) 100 J
Answer: c) 90 J
Explanation: Work done = charge × voltage = 60×1.5=90 J
When velocity is halved, kinetic energy becomes:
a) Half
b) Quarter
c) Same
d) Double
Answer: b) Quarter
Explanation: KE is proportional to square of velocity.
If a body of mass 2 kg is thrown upward with velocity 20 m/s, after 2 s the KE will be:
a) 180 J
b) 100 J
c) 200 J
d) 400 J
Answer: a) 180 J
Explanation: Velocity after 2 s is v=u−gt=20−10×2=0. Kinetic energy at highest point is zero, but if considering velocity just before stopping, KE reduces accordingly.
Work done against friction is always:
a) Positive
b) Negative
c) Zero
d) Infinite
Answer: b) Negative
Explanation: Friction opposes motion, reducing system's kinetic energy.
The work-energy theorem states that work done on a body equals:
a) Change in potential energy
b) Change in kinetic energy
c) Change in momentum
d) Change in power
Answer: b) Change in kinetic energy
Explanation: Work done converts into kinetic energy change.
Power is measured in which unit?
a) Watt
b) Joule
c) Newton
d) Pascal
Answer: a) Watt
Explanation: Watt = Joule per second, SI unit for power.
A body of mass 10 kg is moving at 5 m/s. The kinetic energy is:
a) 50 J
b) 125 J
c) 250 J
d) 500 J
Answer: c) 125 J
Explanation: KE=1/2×10×5^2 =125J
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Chapter wise Extra Q & A Sets (Physics, Class 12) |
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Electric Charges and Fields |
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Electrostatic Potential and Capacitance |
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Current Electricity |
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Moving Charges and Magnetism |
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Magnetism and Matter |
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Electromagnetic Induction |
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Alternating Current (AC) |
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Electromagnetic Waves |
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Ray Optics and Optical Instruments |
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Wave Optics |
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Dual Nature of Radiation and Matter |
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Atoms |
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Nuclei |
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Semiconductor Electronics: Materials, Devices and Simple Circuits |
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Communication System |
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The work done by a force is zero when:
a) Displacement is zero
b) Force is perpendicular to displacement
c) Force is zero
d) All above
Answer: d) All above
Explanation: If any condition doesn't involve force in displacement direction, work done is zero.
Potential energy at ground level is considered:
a) Zero
b) Maximum
c) Infinite
d) Negative
Answer: a) Zero
Explanation: Ground level is reference for potential energy zero.
The energy possessed due to motion is called:
a) Potential energy
b) Kinetic energy
c) Mechanical energy
d) Thermal energy
Answer: b) Kinetic energy
Explanation: Kinetic energy depends on mass and velocity.
The rate of doing work is called:
a) Energy
b) Power
c) Force
d) Momentum
Answer: b) Power
Explanation: Power measures how fast work is done.
A body does 20 J of work in 4 seconds. The power delivered is:
a) 80 W
b) 5 W
c) 10 W
d) 20 W
Answer: b) 5 W
Explanation: Power = Work/time = 20/4 = 5 W.
Mechanical energy in a closed system is:
a) Increasing
b) Decreasing
c) Constant
d) Zero
Answer: c) Constant
Explanation: Energy conservation principle applies in absence of external work.
What is the power of a machine that does 500 J of work in 10 seconds?
a) 50 W
b) 5000 W
c) 5 W
d) 100 W
Answer: a) 50 W
Explanation: Power = 500/10 = 50 W.
The kinetic energy of a body at rest is:
a) Zero
b) Maximum
c) Half of potential energy
d) Infinite
Answer: a) Zero
Explanation: KE requires velocity; zero velocity means zero KE.
Work done is path independent in:
a) Conservative forces
b) Non-conservative forces
c) Frictional forces
d) All forces
Answer: a) Conservative forces
Explanation: For gravity or spring forces, work depends only on initial & final points.
The total energy of an object at height h with velocity v is:
a) mg(h+v)
b) 1/2mv^2+mgh
c) mgh−1/2mv^2
d) mgh
Answer: b) 1/2mv^2+mgh
Explanation: Sum of kinetic and potential energy is total mechanical energy.
When work done by force and displacement are in opposite directions, work done is:
a) Positive
b) Negative
c) Zero
d) Infinite
Answer: b) Negative
Explanation: Opposite directions yield negative work.
The unit of work done in SI is:
a) Watt
b) Newton
c) Joule
d) Pascal
Answer: c) Joule
Explanation: Work is force times displacement; Joule = Newton × meter.
The gravitational potential energy depends on:
a) Mass, height, acceleration due to gravity
b) Velocity only
c) Force only
d) Displacement only
Answer: a) Mass, height, acceleration due to gravity
Explanation: PE=mgh depends on these factors.
