# Homework Help: Urgent: Gravitational Force Problem?

1. Jan 24, 2005

### CinderBlockFist

Hey all, I am stuck on this problem.

A spaceship is ona straight line path between Earth and its mon. At what distance from Earth is the net gravitational force on the spaceship zero?

Well, when I try to use the Universal law of gravitation. F=G(m1)(m2)/r^2, I could find the distance if only I knew the mass of the spaceship, but it is not given. So, I tried to set 2 equations equal, one using the moon, and one using the earth, since the forces would cancel on the spaceship, making it 0. But when i do the computations, I get a negative under a root symbol. Is this the correct approach? Am i missing something here? THanks in advance.

2. Jan 24, 2005

### dextercioby

Your second method is the correct one.Please post your calculations,as to figure out what u're doin wrong...

Daniel.

3. Jan 24, 2005

### CinderBlockFist

Ok, thanks dex, it's kind of lengthy, so since i know this is the correct approach, I'll try to do it more carefully and see what I get, thanks for the quick response.