Answer
(a) decrease
(b) I
Work Step by Step
(a) We know that as the proton moves, it gains kinetic energy. According to the law of conservation of energy, the total energy of the system remains constant. Thus, the gain in kinetic energy is equal to the loss of electric potential energy of the proton. We conclude that the electric potential energy of the proton decreases.
(b) The best explanation is option (I) -- that is, as the proton begins to move, its kinetic energy increases. The increase in kinetic energy is equal to the decrease in the potential energy of the system.
