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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Conservation of mechanical energy holds when:
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Answer: Only conservative forces act
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Coefficient of restitution for a perfectly inelastic collision:
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Answer: 0
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The SI unit of work is:
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Answer: Joule
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Work done by a force F = 5 N over displacement 4 m at angle 60° is:
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Answer: 10 J
Practice Questions
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What are the key concepts in Work, Energy & Power for NEET?
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.
Which formulae are important for Work, Energy & Power in NEET?
Work done: W = Fs cosθ; Kinetic energy: KE = ½mv²; Gravitational PE: PE = mgh; Spring PE: PE = ½kx²; Power: P = W/t = Fv cosθ.
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