How is the Energy Calculated for Two Charged Particles in Orbit?

[Tarabas]

Hi guys. I'm new here.
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.

 

[SteamKing]

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