A point mass `m` is a distance `x` from the centre of mass `M` and radius `R` on its axis. Find the gravitational force between the two. What will this force be if `x gt gt R` and `x lt lt R`? For what value of `x` is the force maximum?

Explanation

In case of sperical shell, the gravitational intensity at a point inside the shell, `I = 0`. So force on particle of mass `m` inside the shell,
`F = mI = 0`