a) Power and efficiency

a) power; the unit watt; P = W/t

b) P = Fv

c) efficiency of a mechanical system; efficiency = useful output energy/total input energy × 100%

power = the rate of work done

P = W/t

• power (W) = energy transferred (J) / time (s)

P = Fv

• power (W) = force (N) × velocity (ms^-1)

efficiency = the percentage of the input energy that is transferred to a useful energy store

efficiency = (useful output energy / total input energy) × 100