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 \(\frac{a}{2}\) distance from the centre, will be : 

\(-3\frac{GM}{a}\)

Gravitational potential at a point \(\frac{a}{2}\) distance from centre = gravitational potential due to spherical shell + gravitational potential due to mass M

V_g = \(-\frac{GM}{a} - \frac{GM}{a/2}\)

    = \(-3\frac{GM}{a}\)