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Homework Help: Moon earth system escape velocity

  1. Apr 18, 2008 #1
    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?
  2. jcsd
  3. Apr 18, 2008 #2
    Certainly. you need an equation for the energy needed to escape from the earth and the moon, and you can add those energies.
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