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Help with Escape Velocity Problem

  1. Jan 25, 2009 #1
    I know that escape velocity is given by v^2 = 2GM/r

    My question is what is the approximate escape speed needed to completely escape the moon & earth's gravity.

    Is it the sum of their individual Escape velocities? or is it one equation, with the radius' added and masses added?

    Thanks
     
  2. jcsd
  3. Jan 25, 2009 #2

    mgb_phys

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    I would add the escape velocities, the value for the moon is pretty small anyway
     
  4. Jan 25, 2009 #3
    Yea I was thinking that something (i.e moons EV) would be negligable since the question asked for the approximate value. But are you sure of that? Wouldn't it make sense astronomically - for something to escape moon's and earths gravity - that's on the moon, to have to travel slightly slower than earth's EV since now we are much farther away?
     
  5. Jan 25, 2009 #4

    mgb_phys

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    I read it to mean at a great distance from both whats the escape velocity, ie. of the earth-moon system, in which case the earth and moon's masses add so you can approx add their escape Vs
     
  6. Jan 25, 2009 #5
    The exact wording of my problem is as follows:

    "assuming one wished to escape completely from both the moon and earth's gravity, what would the approximate escape speed be from the moon?"
     
  7. Jan 25, 2009 #6

    mgb_phys

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    Thats why I would regard it as a single object - and so for a first approximation add the escape Vs
     
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