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Homework Help: Impossible escape velocity question

  1. Mar 31, 2005 #1
    I've got a question in front of me that asks to find the escape velocity for a hypothetical celestial object that has the same density as the sun.

    MC answers are -
    1)2.51 x 10^3 m/s
    2)6.18 x 10^5 m/s
    3)3.08 x 10^5 m/s
    4)5.42 x 10^10 m/s

    As far as I can work out its not possible to find an escape velocity while only knowing the density. I can work out that

    v = 8.873 x 10^-4 x r

    but not find actual v without knowing the radius.
  2. jcsd
  3. Mar 31, 2005 #2


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    Science Advisor

    You are right. The "escape velocity" depends upon the mass not the density.

    If you are not given the radius of the object as well as the density, you cannot find the mass.
  4. Mar 31, 2005 #3


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    Staff Emeritus
    Science Advisor
    Gold Member

    This is a silly question (on their part). If they want you to also assume that it has the same radius as the sun, and you do need a radius to solve this problem, then answer is B. If that is what they want, though, they might as well have asked what the escape velocity from the surface of the sun was.
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