AQA 7408 A Level Physics · Mechanics and Materials
Work, Energy and Power
Treat work as an energy transfer and use the force component parallel to displacement.
Work and energy
For a constant force, W = Fs cos θ, where θ is the angle between force and displacement. Work done by the resultant force equals the change in kinetic energy. The area under a force–displacement graph gives work.
Power
Power is the rate of energy transfer: P = W/t. For steady motion, P = Fv when the force component and velocity are parallel. A large force does not imply large power unless displacement occurs quickly.
Efficiency
Efficiency is useful output divided by total input, using either energy or power consistently. Account for dissipative transfers explicitly and check that the result does not exceed one.