Is it possible that the net kinetic energy for two objects be nonzero while the net momentum is zero? Explain. (0) Explain one difference and one similarity between electric force and the force of gravity. (0) A charge is moved from one point to another in an electric eld. Explain briefly the relationship between electric potential difference and work done in moving this charge. (C) What determines the direction of magnetic force acting on a moving charge? When is the magnitude of the magnetic force zero? (C)