A spaceship of mass m travels from the Earth to the Moon along a line that passes through the center of the Earth and the center of the Moon. At what distance from the center of the Earth is the force due to the Earth twice the magnitude of the force due to the Moon? r = ? m I'm thinking of using the F = Gm1m2/r^2 with G being the gravitational constant and m1 being the mass of the earth, and m2 being the mass of the moon. but i don't know why they say "spaceship of mass m" or if that's even the proper formula to use???