Question

The potential energy of a body at height $h$ is $mgh$. Then its kinetic energy just before hitting the ground is ?

Answer 1

Potential energy is the energy which a body has due to its position or arrangement. The energy is measured relative to a position, we can consider the point to be at zero potential. So for bodies above the surface we take the surfaces as zero potential points, with respect to it we have potential energy as $mgh$ where $h$ is the height above the surface.

Complete step by step answer:
As by law of conservation of energy, energy is neither created or destroyed. Energy only changes its form from one to the other forms. In the question, potential energy of the body is given as $mgh$. When the body falls to hit the ground its potential energy is converted into kinetic energy to follow the law of conservation of mechanical energy. Thus the kinetic energy of the body just before hitting the ground is $mgh$, which was initially at a height $h$ above the surface of earth having potential energy $mgh$.

Note: From the law of conservation of energy the total mechanical energy of a body is the sum of potential and kinetic energy. T.E. $= P.E. + K.E$ which is defined on each and every point in the particle's trajectory. As on the height h body only possesses potential energy and while reaching ground the energy is converted into kinetic energy.