question_answer

A solid sphere of mass 'M' and radius 'a' is surrounded by a uniform concentric spherical shell of thickness 2a and mass 2M. The gravitational field at distance '3a' from the centre will be :           [JEE Main 9-4-2019 Morning]

A)  \[\frac{2GM}{9{{a}^{2}}}\]   

B)       \[\frac{GM}{3{{a}^{2}}}\]

C)  \[\frac{GM}{9{{a}^{2}}}\]                 

D)       \[\frac{2GM}{3{{a}^{2}}}\]

Correct Answer: B

Solution :

[b]

We use gauss's Law for gravitation

(Mass enclosed)

Option [b]