There is a problem I am finding quite confusing: Two particles, with charges of 20.0 nC and -20.0nC, are placed at the points with coordinates (0,4.00cm) and (0,-4.00cm). A particle with charge 10.0 nC is lcoated at the origin. Find the electric potential energy of the configuration of the three fixed charges. I am having difficulty understanding the last sentence. For electric potential energy I thought I would use V = 8.99*10^9(q/r) , where I would sum up each charge? For example: V1 = 8.99*10^9(20nC/4cm) V2 = 8.99*10^9(-20nC/4cm) V3=8.99*10^9(10/0) Then the Electric potential energy would be V1 + V2 + V3 = 0? Or would I use U = 8.99*10^9(q1*q2)/(distance from q1 to q2) and follow the same procedure? I am very confused with the question and what the book refers to as potential energy and electrical potential?? Any help is appreciated! Thanks!