Two concentric spherical shells have masses `M_1 nd M_2` and radii `R_1,R_2(R_(1) lt R_2)` The force exerted by this system on a particle of mass m . If it is placed at a distance `((R_1+R_2)/2)` from the centre .

Explanation

The gravitational force on .m. due to the shell of `M_2` is zero.
The gravitational force on .m. due
`(GM_1m)/(((R_1+R_2)/2))=(4GM_1m)/((R_1+R_2)^2)`