Chapter 19.3, Problem 3EYU

Positive and negative charges of equal magnitude are placed at the upper left and lower right corners of a square, as shown in Figure 19-11. (a) If a positive charge of the same magnitude is placed at the upper right corner of the square, which of the vectors (1, 2, 3, 4) represents the net force exerted on the charge? (b) If the charge at the upper right corner is negative, but with the same magnitude as the other charges, which of the vectors (1, 2, 3, 4) represents the net force exerted on the charge?