posted by Kathrine .
Mars has a mass of about 6.4 X 10^23 kg, and its moon Phobos has a mass of about 9.6 X 10^15 kg. If the magnitude of the gravitational force between the two bodies is 4.6 X 10^15 N, how far apart are Mars and Phobos?
Gravitational force =
G m M/R^2
Look up G (the universal constant of gravity) and solve for R, which is the distance bewteen the centers of Mars and Phobos.