A solid sphere of radius `a` and mass `m` is surrounded by cocentric spherical shell of thickness `2a` and mass `2m` the gravitational field at a distance 3a from their centres is

Options

A. `(GM)/(9a^2)`
B. `(2GM)/(9a^2)`
C. `(GM)/(3a^2)`
D. `(2Gm)/(3a^2)`

Answer

C

Explanation

`E_p=(GM)/((3a)^2)+(G2M)/((3a)^2)+(GM)/(3a^2)`