Two concentric shells of masses `M_(1)` and `M_(2)` are concentric as shown. Calculate the gravitational force on m due to `M_(1)` at points P,Q and `R`.

Explanation

At P,`F = 0`
At Q, `F = (GM_(1)m)/(b^(2))`
At `R`, `F = (G(M_(1))+(M_(2))m)/(c^(2)`.