1. The problem statement, all variables and given/known data A projectile is fired straight away from the moon from a base on the far side of the moon, away from the earth. What is the projectile's escape speed from the earth-moon system? 2. Relevant equations Escape velocity = sqrt[2GM/R] 3. The attempt at a solution What I'm wondering is, do I just have to use this formula the moon or do I have to take the gravitational potential energy of the earth and the projectile into account also?