In the theory of special relativity, the Einstein’s relativistic mechanics is concerned with the motion of particles whose velocities approach the speed of light, but not equal to the speed of massless particle. 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.