28. Consider the four particles shown, with q1 = -40.0 µC, q2 = -20.0 pµC, q3 = 15.0 µC, and q4 = -25 µC. The square has sides of length a = 25.0 cm. %3! 92 B a A a a) What is the change in the electric potential energy of the system of the four charges in the configuration shown in the figure if they were originally infinitely far away? b) Charges q3 and q4 are now moved to points A and B, respectively. What is the change in potential energy of the system after these charges are moved? c) What are the magnitude and direction of the electric field at the location of charge q4 due to the other three charges? d) What is the initial acceleration of the charge q4 due to the electric force exterted by the other three charges on q4 if m4 = 40.0 g? e) With what speed is charge q4 (with m4 = 40.0 g) moving when it is infinitely far away from the other charges?

28. Consider the four particles shown, with q1 = -40.0 µC, q2 = -20.0 pµC, q3 = 15.0 µC, and q4 = -25 µC. The square has sides of length a = 25.0 cm. %3! 92 B a A a a) What is the change in the electric potential energy of the system of the four charges in the configuration shown in the figure if they were originally infinitely far away? b) Charges q3 and q4 are now moved to points A and B, respectively. What is the change in potential energy of the system after these charges are moved? c) What are the magnitude and direction of the electric field at the location of charge q4 due to the other three charges? d) What is the initial acceleration of the charge q4 due to the electric force exterted by the other three charges on q4 if m4 = 40.0 g? e) With what speed is charge q4 (with m4 = 40.0 g) moving when it is infinitely far away from the other charges?