By the theory of special relativity Einstein showed that mass is another form of energy and one can convert mass-energy into other forms of energy, say kinetic energy and vice-versa.Einstein gave the famous mass-energy equivalence relation $E=mc_{2}$ where $c=3×10_{8}m/s$ is the speed of light.

example

Energy equivalent of mass

Energy released if mass of 2 amu is converted into energy is $E=Δmc_{2}$ $=(2×1.67×10_{−27}kg)×(3×10_{8}sm )_{2}$ $=3×10_{−10}J$

definition

Mass Energy Equivalence

The "mass-energy equivalence" principle states that the mass of a system and its energy are the same property in any physical system. This means that anything having mass has an equivalent amount of energy and vice versa.