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

Explanation

The situation given in the question can be pictutised as shown below

Therefore, the magnitudee of gravitational potential at a poinnt situated at a/2 distance from the centre can be given as
`V_(P)=V_("sphere")+V_("particle")=(-GM)/(a)-(GM)/(a//2)=(-3GM)/(a)`.