Abstract
In the Einstein’s theory of special relativity, the relativistic mechanics is concerned with the motion of bodies whose velocities approach the speed of light. It is understood the velocity of a moving particle with mass is less than the speed of velocity and velocity of a massless particle like photon is equal to the speed of light. This paper presents the Einstein’s mass-energy equivalence and the equations of relativistic mass, momentum and energy from the Newton’s second law of motion.