The force f acting on a body with mass m and velocity v is the rate of change of momentum: f − sdydtdsmvd. if m is constant, this becomes f − ma, where a − dvydt is the acceleration. but in the theory of relativity the mass of a particle varies with v as follows: m − m0ys1 2 v 2 yc 2 , where m0 is the mass of the particle at rest and c is the speed of light. show that f − m0a s1 2 v 2 yc 2 d 3y2