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Cheat sheet · Class 11 · CBSE · Science Physics

Work, Energy and Power cheat sheet

The whole chapter on one page: key formulas, facts and the points to remember, for quick revision before a test.

CBSE Class 11 · Physics

Cheat sheet

Chapter 5Work, Energy and Power

Work done by net force = change in kinetic energy (work–energy theorem).

1. Work

W=F⃗⋅d⃗=Fdcos⁡θW = \vec F\cdot\vec d = Fd\cos\theta
W=∫F dxW = \int F\,dx (variable force)

Work is positive for θ < 90°, zero for θ = 90°, negative for θ > 90°.

2. Energy

K=12mv2=p22mK = \tfrac{1}{2}mv^2 = \dfrac{p^2}{2m}
U=mghU = mghUspring=12kx2U_{spring} = \tfrac{1}{2}kx^2

Work–energy theorem: Wnet=ΔKW_{net} = \Delta K.

Conservative force: work independent of path (gravity, spring). Mechanical energy K + U is conserved.

3. Power

P=dWdt=F⃗⋅v⃗P = \dfrac{dW}{dt} = \vec F\cdot\vec v

1 W = 1 J/s; 1 hp = 746 W; 1 kWh = 3.6 × 10⁶ J.

4. Collisions

TypeMomentumKinetic energy
Elasticconservedconserved
Inelasticconservednot conserved
Perfectly inelasticconservedmax loss; bodies stick

1-D elastic, equal masses: velocities are exchanged.

5. Key Points

  • Work by friction is negative.
  • Centripetal force does no work.
  • Spring force F = −kx (Hooke's law).
  • Momentum is conserved in every collision.

Remember: W = Fd cosθ | W_net = ΔK | P = Fv | elastic vs inelastic

Work, Energy and Power: questions and notes

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