Gravitational force between two point masses `m` and `M` separated by a distance `r` is `F`. Now if a point mass `3m` is placed next to `m`, what will be that a. force on `M` due to `m`, b total on `M`?

Explanation

a. If `r` is the distance between two point masses `m` and `M`, then the gravitational force on m due to mass `M` is `F=(GMm)/(r^(2))`.
b. Total force on the body of mass `M` is `F`, i.e.
`F=(GMxx(m+3m))/(r^(2))=(4GMm)/(r^(2))=4F`