MCQ
A solid sphere of uniform density and radius 4 units is located with its centre at the origin $O$ of coordinates. Two spheres of equal radii $1$ unit with their centres at $A(-2,0,0)$ and $B(2,0,0)$ respectively are taken out of the solid leaving behind spherical cavities as shown in figure
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  • A
    The gravitational force due to this object at the origin is zero
  • B
    The gravitational potential is the same at all points on the circle $y^2+z^2=4$
  • C
    The gravitational potential is the same at all points of the circle $y^2+z^2=36$
  • All of the above.

Answer

Correct option: D.
All of the above.
Since cavities are symmetrical w.r.t. O. So the gravitational force at the centre is zero.The radius of the circle $z^2+y^2=36$ is $6.$
For all points for $r \geq 6$, the body behaves as if whole of the mass is concentrated at the centre.
So the gravitational potential is same.Above is true for $z^2+y^2=4$ as well.

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