The question is. There are two particles, one with charge -q and the other with charge Q, and -q particle rotates around the Q particle at a radius r1. What is the Energy at this point? The answer is like this: E= KE + U So now I know that U= -kQq/r1 But according to the answer: KE= kQq/2r1. And I have no idea how they found this KE. Your help would be appreciated. Thanks in advance.