Two spheres, each of radius r, are touching each other. The force of attraction between them is proportional to

Options

A. `r^(6)`
B. `r^(4)`
C. `r^(2)`
D. `r^(-2)`

Answer

B

Explanation

`F=("Gm"_(1)m_(2))/(d^(2)),` where d = 2 r or `F=(G4 pi r^(3)rho)/(3) xx (4 pi r^(3)rho)/(3 xx (2 r)^(2))`
or `F=(G xx 4 pi^(2) rho^(2) r^(4))/(9)`or `F prop r^(4)`