Is it possible to wholly convert a given amount of mechanical energy into thermal energy? Is it possible to wholly convert a given amount of thermal energy into mechanical energy? Cite examples to illustrate your answers.
Solution 12E Step 1 of 3 : Mechanical energy can be completely converted into thermal energy or heat energy. example; friction, Stopping car by hitting brakes. While driving a car,if we hit the brakes. The form of mechanical energy that is all kinetic energy of car will be converted into heat energy. Therefore, Yes is possible to wholly convert a given amount of mechanical energy into thermal energy. Step 2 of 3 : Whereas converting thermal energy into mechanical energy is problematic. According to the 2nd law of thermodynamics- heat cannot be completely converted into other forms of energy . As it places some practical restrictions on the efficiency. example; internal combustion and heat engines. In case of internal combustion engine,most of the energy from the fuel becomes waste heat and only about 20% of the energy from the combustion becomes kinetic/mechanical energy. So it is not very economic to make heat energy to kinetic energy. Or Step 2 of 3 : According to second law not all the heat energy available to a heat engine can be converted into work energy. A machine which converts heat into other forms of energy is called a heat engine. We know that none of the heat engines are 100% efficient.