A particle of mass M is placed at the centre of a uniform spherical shell of equal mass and radius a. Find the gravitational potential at a point P at a distance `a/2` from the centre.

Explanation

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