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Homework Help: Energy in Space

  1. Apr 14, 2009 #1
    1. The problem statement, all variables and given/known data

    A 1250kg meteor rock fragment is momentarily at rest at an altitude of 3000km above the surface of Neptune. Neptune has a mass of 1.03x1026kg and a radius of 2.48x107m.

    Determine: how much work is done on the rock by Neptunes Force of gravity as the rock falls to Neptunes surface (I got the answer to this one it was 3.74x1010J

    I need help on: the velocity with which the rock strikes Neptunes surface

    Not sure where to start with this one.
  2. jcsd
  3. Apr 14, 2009 #2
    If you can find the gravity on Neptune, you can use conservation of energy to determine it's velocity.
  4. Apr 14, 2009 #3
    v= (square root of) 3.74x10^10j/1250kg
    = 7.7X10^4

    But the answer says 7.7X10^3

    Where did i go wrong?
  5. Apr 14, 2009 #4
    The 1/2 magically disappeared. :) You just forgot to multiply by 2, but you got essentially.
  6. Apr 14, 2009 #5
    i screwd up there... when i take half of the 1250kg i get the answer above.
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