Question

Explain by an example that a body may possess energy when it is not in motion.

Answer 1

The energy possessed by a body is called mechanical energy and it may either be due to virtue of its state of motion or due to its position. The energy due to the state of motion is known as kinetic energy and the energy due to the position of the body is known as the potential energy of the body.

Complete step by step answer:
A body possesses energy even when it is not in motion. The only case when a body may not possess any energy is if the body has no mass (that is, mass possessed is zero) along with it being at rest. But a body having no mass cannot exist physically hence the total energy of a body can never be zero. The energy possessed because of the position of the object is known as potential energy. In many instances, we misinterpret potential energy. For example, a boulder kept at the top of the hill, when displaced slightly, falls with some velocity and we can easily perceive that energy, but we also know from energy conservation that energy can neither be created nor be destroyed, only its form can change. So this kinetic energy has come from some ambient or latent energy that the boulder already possessed when it was kept at the top of the hill. This latent or ambient energy is the energy possessed by the boulder at rest and known as potential energy.

Note: The above was the classical physics approach. If we consider the relativistic physics approach, Einstein told us that an object at rest has some energy equivalent to its mass. From this approach, we can say more firmly that an object possesses energy even when it is not in motion.