Energy Efficiency Practice Problems
1. Calculate the energy efficiency of a light bulb that gives of 40J of light from 200J of electrical
energy.
2. Calculate the energy efficiency of a motor that does of 60J of work from 240J of electrical
energy.
3. Calculate the energy efficiency of a radio that gives of 30J of sound from 360J of electrical
energy.
4. Calculate the efficiency of a runner who produces of 500 J of kinetic energy from 2500J of
chemical energy.
5. What is the amount of useful energy from a bulb whose energy efficiency is 25% when
supplied with 600J of energy?
6. The burning gasoline in an engine contains 2000 J of chemical energy. 1200 J of this energy
becomes kinetic energy, and 800 J are lost to friction. What is the energy efficiency of the
engine?
7. A child uses a sling-shot to propel a rock into the air. When the child pulls on the elastic
part of the sling shot, it stores 500 J of energy. When the child lets go, the rock moves
with 400 J of kinetic energy and 100 J are lost to friction. What is the energy efficiency
of this sling shot?