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**1. Homework Statement**

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. Homework 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?