Mechanical energy is the energy of either an object in motion or the energy that is stored in objects by their position. Mechanical energy is also a driver of renewable energy. Many forms of renewable energy rely on mechanical energy to adequately produce power or convert energy. Some everyday examples of mechanical energy are turning a doorknob, breathing in and out, hammering a nail, riding a bicycle, sharpening a pencil, using kitchen appliance, listening to music. The mechanical energy can be converted into two: kinetic energy and potential energy. The expression for kinetic energy is 1/2 mv2 and for potential energy is mgh.

a) An object of mass 40 kg is raised to a height of 5 m above the ground. What is its potential energy? If the object is allowed to fall, find its kinetic energy when it is half-way down.