1. The diagram below show the Sankey diagram for an engine If 106 J of energy are put into the engine how much energy is converted to a. Heat due to friction b. Heat loss c. Useful work Hint: Solution: 2. A car is said to lose about 70% of its energy to heat which is transferred to the cooling system. In the cooling system water is passed around the engine at a rate of about 150 litres per minute.