Question:
A solid sphere of mass ' $M$ ' and radius 'a' is surrounded by a uniform concentric spherical shell of thickness $2 \mathrm{a}$ and mass $2 \mathrm{M}$. The gravitational field at distance '3a' from the centre will be:
Correct Option: , 3
Solution:
(3) $E_{P}=\frac{G M}{(3 a)^{2}}+\frac{G(2 M)}{(3 a)^{2}}=\frac{G M}{3 a^{2}}$
For a part on the surface of a spherical uniform charge
distribution the whole mass acts as a point mass kept at the centre.