Question

What is the gravitational force between two identical 5000 kg asteroids whose centers of mass are seperated by 100 m?

Answer 1

For this question we use the Newtonian relationship F = GMm/r^2.

We often use this relationship when describing one small object orbiting a much more massive one, such as the moon orbiting the Earth. In that case it is obvious that the Earth's mass is M, and the moon's mass is m. In reality it isn't extremely important anyway, but in the case of two identical masses we would ignore the convention.

So, where G is the universal gravitational constant, M = m = 5000kg, and r is the distance between the centres of mass of the two asteroids (100m):

F = GMm/r^2 = (6.67*10^-11)(5000)(5000)/(100^2) = 1.67*10^-7 N.

This answer is to three significant figures. I hope this helps you :)