A particle of mass 'm' is kept at rest at a height 3R from the surface of earth , where 'R' is radius of earth and 'M' is mass of earth .The minimum speed with which it should be projected , so that it does not return back ,is (g is acceleration due to gravity on the surface of earth )

Options

A. `[(GM)/R]^(1/2)`
B. `[(GM)/(2R)]^(1/2)`
C. `[(gR)/4]^(1/2)`
D. `[(2g)/R]^1/2`