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

Answer

c

Explanation

`E_(p)= (GM)/((3a)^(2))+(G(2M))/((3a)^(2))= (GM)/((3a)^(2))`

For a part on the surface of a spherical uniform charge distribution the whole mass acts as a point mass kept at the centre.