Cars are a major source of greenhouse gases and are also one of the main consumers of fossil fuels. To help combat this Toyota released the "Prius" in 2001,a hybrid

petrol-electric car with a petrol engine aided by an electric motor. It uses only half the fuel of a normal car and emits half the carbon dioxide (if you use electricity from renewable energy sources). One of the reasons it is so efficient is that energy which is usually lost as heat during braking is used to run a generator charging the battery, which then runs the electric motor. i) Can a given amount of mechanical energy be transferred completely into heat? If so, give an example. If not, why not? ii) Can heat be transferred completely into mechanical energy? If so, give an example. iii) What are the implications of this for engines, and in particular hybrid cars?