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Homework Help: Gravitational Potential Energy of Envelope around star

  1. Sep 20, 2009 #1
    I am confused about this question:

    A giant star has a radius of 200 Rsun, with core of mass 0.6 Msun surrounded by an extended envelope of mass 0.2 Msun.
    (a) Estimate the gravitational potential energy of the envelope.

    When it says the envelope, does this mean the 'shell' surrounding the interior, where you can use the conservation of mass equation of a shell => dm/dr = 4pi*p*r^2 and Plugging it into Gravitational potential energy equation: dU = -[G M(r)*dm]dr/r. In this case dm is the mass of envelope and M(r) is 0.6Msun and r would be 200Rsun. Not sure what dr would be, since it is the thickness of the envelope. Thanks
  2. jcsd
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