Show that a necessary condition for a system to be in equilibrium under the conditions of the potential shown in Fig. 13.4, it must be at the position corresponding to the coordinates of point \(\mathrm{A}\), or \(\mathrm{B}\), or \(\mathrm{C}\). Are there other equilibrium points in the region of \(r\) shown in Fig?

 Fig. 13.4

11 12 V(r) A B E3 E2 C 15 16 E Eo