The gravitational force between two masses is given by:
[tex]F=G \frac{m_1 m_2}{r^2} [/tex]
where
G is the gravitational constant
m1 and m2 are the two masses
r is the separation between the two masses
We see that the force is proportional to the inverse of the square of the distance: [tex]F \sim \frac{1}{r^2} [/tex]
therefore, if the distance is tripled:
r'=3r
The force decreases by a factor 1/9:
[tex]F \sim \frac{1}{(3r)^2}= \frac{1}{9} \frac{1}{r^2} [/tex]
Since the original force was 36 N, the new force will be
[tex]F' = \frac{1}{9} (36 N)= 4 N [/tex]
