4. (50 points) A right-triangular ionic compound is fixed in space, and is comprised of two positive charges with the same magnitude, 91, separated by a distance a, and a negative ion with charge q2 < 0 located a distance b away from one of the positive charges. A fourth charge, q3 < 0, is placed a horizontal distance, a, from the bottom charge 91 (see the diagram). For this problem the y-axis points upward, and the x-axis points to the right. a q1 b 91 93 Figure 4: charge diagram 92 a. (15 points) What is the electric field (magnitude and direction with respect to the positive x-axis) at the location of q3 due to the ionic compound? b. (10 points) What is the force (magnitude and direction with respect to the positive x-axis) exerted on q3 due to the ionic compound? c. (15 points) What is the electric potential energy associated with q3 in the presence of the ionic compound? d. (10 points) What is the total electric potential energy associated with the configuration of charges shown in the diagram?