A particle with charge Q coulomb, tied at the end of an inextensible string a length R meter, revolves in a vertically plane. At the centre of the circular trajectory there is a fixed charge of magnitude Q coulomb. The mass of the moving charge M is such that `Mg=(Q^(2))/(4pi epsi_(0)R^(2))` if at the highest position of the partical the tnesion of the string just vanishes, the horizontal velocity at the lowest point base to the

Options

A. 0
B. `2sqrt(gR)`
C. `sqrt(2gR)`
D. `sqrt(5gR)`