17.71. Set Up: The ball is in equilibrium, so for it and The force diagram for the ball is given in Figure 17.71. is the force exerted by the electric field. Since the electric field is horizontal, is horizontal. Use the coordinates shown in the figure. The tension in the string has been replaced by its x and y components. Figure 17.71 Solve: gives and gives so q is negative and is to the right, so is to the left in the figure. Reflect: The larger the electric field E the greater the angle the string makes with the wall. 17.72. Set Up: is toward a negative charge and away from a positive charge. At the origin, due to the charge is in the direction, toward the charge. Solve: (a) so is away from Q so Q is positive. gives (b) so is toward Q so Q is negative. 17.73. Set Up: The gravity force (weight) has magnitude and is downward. The electric force is Solve: (a) To balance the weight the electric force must be upward. The electric field is downward, so for an upward force the charge q of the person must be negative. gives
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This note was uploaded on 03/06/2009 for the course PHYS 114 taught by Professor Shoberg during the Spring '07 term at Pittsburg State Uiversity.