A ball of mass m enters the loop at A with velocity v as shown in the above figure. Loop radius is R and acceleration due to gravity is g. What should be the maximum velocity v so that ball does not reach the point B?
(a)$\frac{\sqrt{gR}}{2}$ (b)$\sqrt[2]{gR}$ (c) $\sqrt{2gR}$ (d) None of the above