If an electric motor uses 50 kJ of energy to do 46 kJ of work, how efficient is it?
Efficiency is calculated as the ratio of useful output energy to input energy. In this case, the useful output energy is the work done by the motor, which is 46 kJ.
Efficiency = (useful output energy / input energy) x 100%
Efficiency = (46 kJ / 50 kJ) x 100%
Efficiency = 0.92 x 100%
Efficiency = 92%
Therefore, the efficiency of the electric motor is 92%.