Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Star Masses and Radius

  1. Dec 1, 2009 #1
    Sorry noone was answering my question, and I just wanted to get this done:

    1. The problem statement, all variables and given/known data
    ...Hence show that the mass of the star is M = [tex]4\pi[/tex][tex]p_{c}[/tex][tex]\left(R^{3}/3 )[/tex]



    2. Relevant equations
    M(r) = [tex]4 \pi[/tex][tex]p_{c}[/tex][tex]\left(r^{3}/3 - r^{4}/4R)[/tex]
    This is the mass within a radius


    3. The attempt at a solution
    I already found the mass within a radius via intergration (look at relevant equations), and I know that I have to build up an 'infinite' number of radial masses to get the whole mass of the star. But do I use integration on this equation or something else? What do I do?
     
  2. jcsd
  3. Dec 1, 2009 #2
    Oohh for f_cks sake.... I realised

    Total radius of the star is 'R'. Just substitute that in for [tex]r[/tex] and cancel, since r1 is subjective and doesn't factor for the whole star.

    WHHHYYYYYY!??
     
  4. Dec 2, 2009 #3

    Matterwave

    User Avatar
    Science Advisor
    Gold Member

    The total mass of anything is just M=pV where p is the average density and V is the volume. Here V=4/3*pi*R^3. That's that...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook