Question

Mars has a mass of about 6.45 × 10
23
kg,
and its moon Phobos has a mass of about
9.4 × 10
15
kg.
If the magnitude of the gravitational force
between the two bodies is 4.68 × 10
15
N,
how far apart are Mars and Phobos? The
value of the universal gravitational constant
is 6.673 × 10
−11
N · m2
/kg
2

Answer 1

All you have to do is solve the gravitational attraction equation for R:

F = 4.68 × 10^-15 N = G m*M/R^2

where
G = 6.673 × 10^−11 N·m^2/kg^2
m = Phobos' mass
M = Mars' mass

Answer 2

R^2=G*M*m/F
or,R=(G*M*m/F)^1/2