20. It is known that the force F acting on a body of mass m is given by d F = = [mv] dt where v is the velocity of the particle. However, Einstein's Theory of Relativity says that the mass of the body varies with v according to the law mo m = (1-2) 1/2 where c is the speed of light and mo is the mass of the body at rest. Show that amo (1 - 2)3/2* where a is the acceleration of the particle at time t. F=