1. Answer as best as possible:

a. Three point-like charges are placed at the corners of a rectangle as shown in the figure, a = 28.0 cm and b = 68.0 cm.

Find the minimum amount of work required by an external force to move the charge 91 to infinity. Let 91 = +2.10 MC, 92

= -2.80 MC, 93 = -3.20 MC.

b. Four point-like charges are placed as shown in the figure, a = 28.0 cm and b = 68.0 cm. Find the electric potential

energy of the entire system of charges. Let 91 = -2.10 MC, 92 = +2.80 MC, 93 = +3.20 MC, and 94 = - 9.00 MC

c. Three point-like charges are placed as shown in the figure, a = 38.0 cm and b = 58.0 cm. The charge (93) is placed

half way on the (b) side. Find the electric potential energy of the charge 92. Let q, = - 1.80 C, q, = -2.20 uC, and 93 =

-5.00 uC.