Answer to Question #331398 in Electricity and Magnetism for ruzzel

Question

A point charge q1, is held stationary at the origin. A second charge q2 is placed at a point a, and the electric potential energy of the pair of charges is −6.4×10 −8J. When the second charge is moved to point b, the electric force on the charge does 4.2×10 −8 J of work. What is the electric potential energy of the pair of charges when the second charge is at point b?

Answer 1

$U=U_2-U_1=10.6\cdot10^{-8}~J.$