Work, Energy & Power — A/L Physics

What must I remember about Work, Energy & Power?

• Work Done: W = F · s = F s cos θ; Work is scalar; Work done is positive when θ < 90°, zero when θ = 90° (e.g., centripetal force), and negative when θ > 90° (e.g., friction).
• Kinetic Energy & Gravitational Potential Energy: KE = (1/2)mv²; PE = mgh; Elastic Potential Energy in stretched spring/wire = (1/2)kx² = (1/2)Fx.
• Work-Energy Theorem: The net work done by all forces acting on a particle equals the change in its kinetic energy: W_net = ΔKE = (1/2)mv² - (1/2)mu².
• Power: Rate of doing work: P = dW/dt = F · v; Average Power P_avg = W / t; Efficiency η = (Useful Power Output / Total Power Input) * 100%.

Test yourself (1 minute)

1. Conservative vs Non-Conservative Forces

   For conservative forces (gravity, electrostatic, spring), work done around a closed path is zero (∮ F · dr = 0) and path-independent; Non-conservative forces (friction, drag) dissipate energy as heat.

2. Law of Conservation of Mechanical Energy

   In an isolated system governed strictly by conservative forces: E_total = KE + PE = Constant.

3. Power in vehicle motion

   At maximum terminal velocity on level road: Engine driving force F equals total resistive resistance R (F = R), hence P = R * v_max.

Practise Work, Energy & Power questions today

Source: NIE G.C.E. (A/L) Physics Resource Book - Unit 2: Mechanics

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Where does Work, Energy & Power fit in the syllabus?

Unit 2.4 · Year 1 · Term 1