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Work, Energy & Power
Work-energy theorem, conservation of energy, collisions
Key Concepts
- Work is done only when force has a component along displacement
- Work–energy theorem: net work = change in kinetic energy
- Conservative forces: work done is path-independent (gravity, spring)
- Elastic collision: both KE and momentum conserved
- Inelastic collision: momentum conserved, KE not conserved
Important Formulae
| Work done | W = Fs cosθ |
| Kinetic energy | KE = ½mv² |
| Gravitational PE | PE = mgh |
| Spring PE | PE = ½kx² |
| Power | P = W/t = Fv cosθ |
Quick Tips
- Work done by friction is always negative (opposes motion).
- In perfectly inelastic collision, bodies stick together — maximum KE is lost.
- 1 horsepower = 746 W.
Sample Practice Questions
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A body of mass 10 kg is moving at 5 m/s. Its kinetic energy:
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Answer: 125 J
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Power of an engine that lifts 200 kg to height 10 m in 5 s (g=10):
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Answer: 4000 W
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Work done against gravity on moving mass m to height h is:
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Answer: mgh
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A spring of spring constant k is compressed by x. Potential energy stored:
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Answer: ½kx²
Practice Questions
Practice 20 randomly selected NEET questions on Work, Energy & Power. Answers are revealed after each question.
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