JEE Main & Advanced
JEE Main Paper (Held on 09-4-2019 Morning)
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 :
We use gauss's Law for gravitation \[g.4\pi {{r}^{2}}=\](Mass enclosed)\[4\pi G\] \[g=\frac{3M4\pi G}{4\pi {{(3a)}^{2}}}\]\[=\frac{MG}{3{{a}^{2}}}\] Option [b]