There is an insulator rod of length L and of negligible mass with two small balls of mass m and electric charge Q attached to its ends. The rod can rotate in the horizontal plane around a fixed vertical axis crossing it at a distance L/4 from one of its ends. At first the rod is in unstable equilibrium in a horizontal uniform electric field of field strength E. Then we gently displace it from this position. Determine the maximum velocity attained by the ball that is closer to the axis in the subsequent motion.
(1) m2QEL
(2) 5m2QEL
(3) 5mQEL
(4) 5m4QEL