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 delivered to an object (W) = energy transferred to the object (J) / time (s)

P = Fv

• power delivered to an object (W) = force applied on the object (N) × velocity of the object (ms^-1)

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

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