A particle of mass M is situated at the centre of a spherical shell of same mass and radius a. The gravitational potential at a point situated at `a//2` distance from the centre, will be

Explanation

The gravitational potential at the point P due to the particle at the centre is `V_(1) = (GM)/(a//2)=-(2GM)/a`
The potential at P due to the shell is `V_(2) = - (Gm)/a`
The net potential at P is `V_(1)+V_(2) = - (3Gm)/a`