Q. Two small beads having positive charges 3q and q are fixed at the opposite ends of a horizontal, insulating rod, extending from the origin to the point x = d, a third small charged bead is free to slide on the rod. At what position is the third bead in equilibrium? Can it be in stable equilibrium?
Q. The two spheres in the figure are charged. Each has a mass of 0.30 kg. The lower mass is rigidly attached to the floor, with a charge of -2.1 x 10-5 C. The mass above it is held to the ceiling with a string, whose tension is 1.8 N. The masses are 0.1 m apart. What is the charge on the upper sphere (and make sure you get the sign right)?