Four equal point charges, Q, are fixed at the corners of a square of side b. (a) What istheir total electrostatic potential energy? (b) How much potential energy will a fifth charge, Q, have at the center of the square (relative to V=0 a r =∞)? (c) If constrained to remain in that plane, is the fifth charge in stable or unstable equilibrium? (d) If a negative (-Q) charge is at the center, is it in stable equilbrium?