Sample Problem

If a moon feels an attractive force 80,000N from a planet, what kind of force will the planet feel from the moon if the distance between them is doubled?



Based on the equation F = G (m1 m2) /r2 , we see that the force will decrease by a factor of 4 if the radius is doubled. The planet will feel a force of 20,000N from the moon (the planet and the moon will feel equal forces because of Newton’s third law)