A force is required to do work. The work done by a force is the product of displacement and the component of force in the direction of displacement. Prove this statement.

Force is required to lift a body from the ground to a height h and work is measured as the product of force and magnitude of displacement. A man of mass 60 kg carries a stone of mass 20 kg to the top of a multistoreyed building of height 50 m . Calculate the total energy spent by him? (g= 9.8 m/s^2)