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Homework Help: Gravitational Potential Energy of astronaut

  1. Nov 19, 2005 #1
    A 120kg astronaut stands on the surface of an asteroid of radius 600m. The astrunaut leaves the surface with 15J of kinetic energy and reaches a maximum height of 300m above the surface. What is the mass of the asteroid? (Answer: 3.4*1012kg)

    At the maximum height, all of the kinetic energy becomes potential gravitational energy.

    EK = Epg
    15 = Gmm'/r
    15 = 6.67*10-11*120*m'/(300+600)
    1.7*1012kg = m'

    I think there's an error in the calculation somewhere because my answer is exactly half the correct answer but I can't figure out what I'm doing wrong.
  2. jcsd
  3. Nov 19, 2005 #2
    I don't know but at first sight, you don't take into account the pot. energy at the surface-...does this make sense, like : Kinetic+potenial=converved=15-Gmm'/600=0-Gmm'/900 ??
  4. Nov 19, 2005 #3


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    Homework Helper
    Gold Member

    Remember, you want the change in potential energy, not the potential energy itself.
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