The energy of a particle was correctly calculated by Einstein in the Theory of Relativity to be E = mc2 p 1−v2/c2 (1) where m is the rest mass of the particle. What if a particle is at rest (i.e. it isn’t moving so v = 0)? Then, E = mc2. This is Einstein’s famous equation for the rest energy of a particle. Even a particle that isn’t .... Initially, a particle is moving at 4.00 m/s at an angle of 33.5 degrees above the horizontal. Two seconds later, its velocity is 6.45 m/s at an angle of 60.0 degrees below the horizontal. What was the particle's average acceleration during these 2.00 . Math. A particle P starts at the origin (x0,y0)=(0,0), of the plane. "/>A particle initially at rest starts moving from