is obtained.) IS 21.76, Two identical spheres are each attached to silk threads of length L = 0.500 m and hung from a common point (Fig. 21.44). Each sphere has mass m = 8.00 g. The radius of each sphere is very small compared to the distance between the spheres, so they may be treated as point charges. One sphere is given positive charge 9i, and the other a different positive charge 42; this causes the spheres to separate so that when the spheres are in equilibrium, each thread makes an angle 0 = 20.0 with the vertical. (a) Draw a free-body diagram for each sphere when in equilibrium, and label all the forces that act on each sphere. (b) Determine the magnitude of the electrostatic force that acts on each sphere, and determine the tension in each thread. (c) Based on the information you have been given, what can you say about the magnitudes of 4, and 92? Explain your answers. (d) A small wire is now connected between the spheres, allowing charge to be transferred from one sphere to the other until the two spheres have equal charges; the wire is then removed. Each thread now makes an angle of 30.0 with the verti- cal. Determine the original charges. (Hint: The total charge on the pair of spheres is conserved.) 42