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Homework Help: Star Equations & Derivations

  1. Jan 18, 2008 #1
    Right I've got an exam at half past 4, tomorrow on a Saturday! I've spent the past few days doing past exam questions and a lot of them I'm able to do or at least work out for myself after a bit of time. Here's a couple I'm really stuck on so some help would be really really appreciated.

    1. The problem statement, all variables and given/known data
    *all = signs are proportional not equal. I thought it'd be easier than sticking k's everywhere.

    Combine equations [1] and [2] to show to a good approximation that T = R^2
    Assume that all these stars have the same average density.

    2. Relevant equations
    [1] L = M^3.3
    [2] L = R^2*T^4

    3. The attempt at a solution
    Don't really know where to start with this one. I've tried re-arranging all of the equations and substituting in, but I always get stuck very early on. Mathmatical derivations really aren't my strong point.

    On a similar vain, I have this equation.

    Show that L = T^B and derive the value of B
    (I know B is ~-0.7 btw, I just don't know how to derive that)
    again = is actually proportional
  2. jcsd
  3. Jan 18, 2008 #2


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    Homework Helper

    How is the mass related to volume and volume to radius?

    and use "Assume that all these stars have the same average density."
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