Question

A spherical ball of mass $m$ with charge q can revolve in a vertical plane at the end of string of length $l.$ At the centre of revolution, there is a second ball with a charge identical in sign & magnitude to that of the revolving ball. What minimum horizontal velocity must be imparted to the ball in the lowest position to enable it to make a full revolution?

Answer 1

For the lowest most position,

$v=2\sqrt{gR}$

given,

$\therefore v=2\sqrt{gl}$ m/s