Work, Energy and Power is a Class 11 Physics chapter in the NEET (UG) syllabus. NEET720 has 907 reviewed practice questions on it, each with a quick answer and a step-by-step explanation. The 8 questions below are free and fixed, so you can bookmark this page; the full chapter, plus mistake tracking and spaced revision, is in the app.
182
easy
576
medium
149
hard
Topics covered
Work Done by Variable Force · Kinetic Energy and Momentum · Work Done at an Angle · Conservation of Mechanical Energy · Vertical Circular Motion Energetics · Work Done by Friction · Rolling and Energy · Work Done Against Gravity · Kinetic and potential energy · Work by constant and variable forces · Kinetic energy and work-energy theorem · Potential energy and conservation of energy · Power · Collisions · Motion in a vertical circle · Conservation of energy and momentum · WET · Work-energy theorem with friction · PE · POW · COLL · VERT · Collisions and energy conservation · Work by variable/centripetal forces · Work-energy from graphs · Energy conservation with friction and springs · Collisions -- limiting cases · Power in machines · Elastic potential energy from experimental data · Collisions -- statement evaluation · Power for vehicles on inclines · Power and pumping · Vertical circular motion with energy conservation · Work by normal reaction on curved surfaces · Work-energy theorem from force graphs · Spring potential energy -- limiting case · Collisions -- diagnosing a worked solution · Definitions of power · Energy loss to friction on inclines · Energy loss in a swinging pendulum
8 free Work, Energy and Power practice questions with answers
Choose an answer in your head before opening it. Each explanation says why the correct option is right and, where relevant, why the tempting wrong option is wrong.
Question 1 · medium · Potential energy and conservation of energy
The gravitational potential energy of a ball held at height h above the ground is most correctly described as a property of
- A.the ball alone
- B.the Earth-ball system as a whole
- C.the ball's motion, since it is a form of kinetic energy
- D.the gravitational field alone, independent of the ball's mass
Show answer and explanation
Answer: B. the Earth-ball system as a whole
Gravitational PE arises from the mutual interaction between the Earth and the ball; it is meaningful only as a property of this two-body system's configuration, not of the ball in isolation.
Potential energy in general is associated with the configuration of an interacting system, not with any single member of it. For a ball near the Earth's surface, gravitational PE = mgh is conventionally attributed to 'the ball' as a shorthand, but physically it belongs to the Earth-ball system because it arises from their mutual gravitational interaction — if the Earth were absent, there would be no such PE regardless of the ball's height. It is not kinetic energy (which depends on velocity, not position) and it explicitly depends on the ball's mass, ruling out D.
Common mistake: Treating PE as though it belongs solely to the raised object, independent of the Earth.
Question 2 · medium · Potential energy and conservation of energy
A block slides down a rough incline and reaches the bottom with less kinetic energy than it would have gained on a smooth incline of the same height. The 'missing' mechanical energy has
- A.vanished, since friction destroys energy
- B.been converted entirely into gravitational potential energy stored elsewhere
- C.been converted into heat (and some sound) at the sliding surfaces, so total energy including this thermal energy is still conserved
- D.reduced the effective mass of the block for the rest of the motion
Show answer and explanation
Answer: C. been converted into heat (and some sound) at the sliding surfaces, so total energy including this thermal energy is still conserved
Friction is non-conservative: it converts organized mechanical energy into disorganized thermal energy (and some sound), which is real energy that still obeys overall conservation of energy — only mechanical energy (KE + PE) is not conserved.
The law of conservation of energy is universal; what fails here is conservation of mechanical energy specifically, because friction is a non-conservative force. The mechanical energy 'lost' by the block is not destroyed — it is transformed into heat at the block-incline interface (raising their temperatures slightly) and some sound energy. If this thermal/sound energy is included, total energy is exactly conserved. This is the standard resolution of apparent energy loss whenever friction, air resistance, or other dissipative forces act.
Common mistake: Thinking energy 'disappears' when a non-conservative force acts.
Question 3 · medium · Potential energy and conservation of energy
A particle experiences both a spring force and a kinetic friction force during a displacement. Regarding energy accounting for the two forces, which statement is correct?
- A.The work done by the spring force depends on the path taken, just like friction
- B.The work done against friction can be fully recovered as elastic PE if the particle retraces its path
- C.The work done by the spring force can be fully recovered as elastic potential energy, but the work done against friction is permanently lost as heat
- D.Both forces conserve the particle's total mechanical energy identically
Show answer and explanation
Answer: C. The work done by the spring force can be fully recovered as elastic potential energy, but the work done against friction is permanently lost as heat
The spring force is conservative — its work is stored as recoverable elastic PE — while kinetic friction is non-conservative and always converts mechanical energy irreversibly into heat.
A spring force is conservative: work done against it is stored as elastic potential energy and can be fully recovered (e.g. the block regains its speed as the spring pushes back). Kinetic friction, however, is non-conservative: work done against it is converted into heat at the contact surfaces and cannot be recovered as useful mechanical energy, regardless of whether the particle retraces its path. This distinction is why only conservative forces admit a potential energy function.
Common mistake: Believing friction's effect can be undone by retracing the path.
Question 4 · medium · Potential energy and conservation of energy
A ball is thrown vertically upward and returns to the thrower's hand. Considering only the interval from release to being caught, and ignoring air resistance, which statement about its gravitational potential energy is correct?
- A.PE keeps increasing throughout the flight, both going up and coming down
- B.PE increases going up, decreases coming down, and returns to its initial value when the ball is caught
- C.PE remains constant throughout, because mechanical energy is conserved
- D.PE at the highest point equals the ball's total mechanical energy only if it was thrown with the minimum possible speed
Show answer and explanation
Answer: B. PE increases going up, decreases coming down, and returns to its initial value when the ball is caught
Height rises then falls back to the starting point, so PE rises then falls back to its initial value; total mechanical energy (KE+PE) stays constant throughout, but PE alone does not.
As the ball rises, its height above the hand increases, so PE increases, reaching a maximum at the highest point (where KE = 0, so PE there equals the total mechanical energy, regardless of the initial speed — this holds for any launch speed, making option D's extra condition wrong). As the ball falls back, height decreases and so does PE, returning to its initial value exactly when the ball reaches the hand again. Total mechanical energy stays constant throughout (ignoring air resistance), but this does not mean PE alone is constant — KE and PE trade off continuously.
Common mistake: Assuming energy conservation means every form of energy individually stays constant.
Question 5 · medium · Potential energy and conservation of energy
A block slides down a rough incline and comes to rest exactly at the bottom, with all of its initial gravitational PE dissipated by friction. A student claims: 'Since all the mechanical energy is lost, energy is not conserved in this process.' This claim is
- A.correct, since the block's mechanical energy decreased to zero
- B.incorrect — the mechanical energy that disappeared reappears as heat (thermal energy) in the block and incline, so total energy is still conserved
- C.correct, because friction is known to destroy energy permanently
- D.incorrect, but only because some of the missing energy was converted into extra momentum given to the incline
Show answer and explanation
Answer: B. incorrect — the mechanical energy that disappeared reappears as heat (thermal energy) in the block and incline, so total energy is still conserved
Friction converts mechanical energy into heat at the sliding interface; total energy (mechanical + thermal) is exactly conserved even though mechanical energy alone is not.
The general law of conservation of energy holds in every physical process. What is lost here is specifically mechanical energy (KE + gravitational PE), which is not conserved whenever a non-conservative force like friction acts. The 'missing' energy reappears as heat generated at the block-incline interface (and possibly a little sound), raising their internal (thermal) energy. Including this thermal energy, the total energy of the system is exactly conserved — nothing is destroyed.
Common mistake: Treating the disappearance of mechanical energy as a violation of energy conservation itself.
Question 6 · medium · Work by constant and variable forces
A block is given a push so that it slides up a rough incline, momentarily stops, and slides back down to its starting point. Considering the entire round trip, the work done by friction on the block is
- A.zero, because the net displacement is zero
- B.negative during both the upward and the downward journey
- C.negative going up but positive coming down, since friction reverses direction
- D.positive during both journeys
Show answer and explanation
Answer: B. negative during both the upward and the downward journey
Kinetic friction always acts opposite to the sliding velocity, so it does negative work on both legs; the round-trip friction work is negative, which is why the block returns slower than it left.
Going up, the block slides up-slope, so friction acts down-slope: work negative. Coming down, the block slides down-slope, so friction acts up-slope: again opposite to displacement, work negative. The total work by friction over the closed path is therefore negative, not zero — friction is non-conservative, and its closed-path work equals the mechanical energy converted to heat. Option C's error is subtle: the friction force does reverse, but so does the displacement, so the product remains negative on both legs.
Common mistake: Claiming zero work over a closed path as if friction were conservative.
Question 7 · easy · Work done by a force
A force of 50 N is applied on a block, making an angle of 60 degrees with its displacement of 20 m. Find the work done by this force.
- A.250 J
- B.500 J
- C.1000 J
- D.866.03 J
Show answer and explanation
Answer: B. 500 J
W = Fd cos(theta) = 500 J.
Work done by a constant force is W = F d cos(theta), where theta is the angle between force and displacement. Here W = 50 x 20 x cos(60 deg) = 1000 x 0.5 = 500 J.
Common mistake: Forgetting the cos(theta) factor, or confusing it with sin(theta).
Question 8 · easy · Work done by a force
A force of 30 N is applied on a block, making an angle of 37 degrees with its displacement of 15 m. Find the work done by this force.
- A.270.82 J
- B.179.69 J
- C.359.39 J
- D.450 J
Show answer and explanation
Answer: C. 359.39 J
W = Fd cos(theta) = 359.39 J.
Work done by a constant force is W = F d cos(theta), where theta is the angle between force and displacement. Here W = 30 x 15 x cos(37 deg) = 450 x 0.7986 = 359.39 J.
Common mistake: Forgetting the cos(theta) factor, or confusing it with sin(theta).
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Questions about Work, Energy and Power for NEET
How many NEET questions does NEET720 have on Work, Energy and Power?＋
NEET720 has 907 reviewed practice questions on Work, Energy and Power (Physics): 182 easy, 576 medium and 149 hard. 8 of them are free on this page with full explanations; the rest are available in the app.
Is Work, Energy and Power a Class 11 or Class 12 chapter for NEET?＋
Work, Energy and Power is a Class 11 Physics chapter in the NEET (UG) syllabus. Read the NCERT chapter first, then practise chapter-wise MCQs and previous-year questions.
How should I practise Work, Energy and Power for NEET?＋
Attempt the questions below without looking at the options for more than a few seconds, mark your answer, then read the explanation even when you were right. Record every mistake and revisit it after a gap. On NEET720 this happens automatically: wrong answers go to your Mistake Book and are scheduled for spaced revision.
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Questions are original NEET720 compositions reviewed for correctness, syllabus fit and option quality. Counts update as the bank grows (907 active practice questions in this chapter today).