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.   Cambridge Open Engage, Cambridge University Press and DOI