2. A uniform insulating rope of mass M and length L hangs from a ceiling. A small metal ball with charge +Q and mass m is suspended at the bottom of the rope, which is above an infinite grounded plane at a distance d from it, as shown in Figure 6. There are surface charges induced in the grounded plane. (a) Find the electric force acting on the charged metal ball. (b) The surface charge density at point O, which is directly below the ball. (c) Find the speed of a transverse wave on the rope due to the electric and gravitational forces, which is a function of y, the distance from the lower end. (15%) [Hint: the speed of a transverse wave on a string v = with tension τ and linear mass density μ.]