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//d)=(-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`