1. Four lightweight balls A, B, C, and D are suspended by threads. Ball A has been touched by a plastic rod that was rubbed with wool. When the balls are brought close together, without touching, the following observations are made: . Balls B, C, and D are attracted to ball A. . Balls B and D have no effect on each other. - Ball B is attracted to ball C. What are the charge states (positive, negative, or neutral) of balls A, B, C, and D? Explain. 7. Each part of Figure (2121.7IEI shows one or more point charges. The charges have equal magnitudes. If a positive charge is moved from position i to position f, does the electric potential energy increase, decrease, or stay the same? Explain. Figure 021.7 (a! (b) I\" 68. | | | | I INT Two 3.0 g spheres on 1.0-m-long threads repel each other after being equally charged, as shown in Figure 1320.689. What is the charge q? Figure P20.68 7. | | | Two identical metal spheres A and B are in contact. Both are initially neutral. 1.0 X 1012 electrons are added to sphere A, then the two spheres are separated. Afterward, what are the charge of A and the charge of B? 61. | I | | Figure 1320.615I shows four Charges at the corners of a square of side L. What magnitude and sign of charge Q will make the force on charge q zero? Figure P20.6 1