A point charge Q = +4.60 C is held fixed at the origin. A second point charge

Question:

A point charge Q = +4.60 µC is held fixed at the origin. A second point charge q = + 1.20 µC with mass of 2.80 X 10-4 kg is placed on the x-rods, 0.250 m from the origin.
(a) What is the electric potential energy U of the pair of charges? (Take U to be zero when the charges have infinite separation.)
(b) The second point charge is released from rest. What is its speed when its distance from the origin is (i) 0.500 m; (ii) 5.00 m; (iii) 50.0 m?