(a) Starting from Coulomb's law, show that the electric potential a distance r from a point charge q is given by V = q/4pie0r (b) Four point charges are assembled as shown in Fig. 11.2. Calculate the potential energy of this configuration (you may assume that the charges are isolated and in a perfect vacuum). Does the potential energy depend upon the order in which the charges are assembled? (c) Is the charge configuration in (b) stable?