There is a non-conducting rod of length $L$ and negligible mass with two small balls each of mass $m$ and electric charge $Q$ attached to its ends. The rod can rotate in the horizontal plane about a fixed vertical axis crossing it a distance $\frac{L}{4}$ from one of its ends. A uniform horizontal electric field $E$ (along $+x$ axis) is established. At first the rod is in unstable equilibrium. If it is disturbed slightly from this position, the maximum velocity attained by the ball which is closer to the axis in subsequent motion, is

There is a non-conducting rod of length $L$ and negligible mass with two small balls each of mass $m$ and electric charge $Q$ attached to its ends. The rod can rotate in the horizontal plane about a fixed vertical axis crossing it a distance $\frac{L}{4}$ from one of its ends. A uniform horizontal electric field $E$ (along $+x$ axis) is established. At first the rod is in unstable equilibrium. In what position, the rod must be set so that if displaced a little from that position, it begins simple harmonic oscillations about the axis?