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Universal Gravitation and neutron stars

  1. Dec 1, 2009 #1
    1. The problem statement, all variables and given/known data
    Certain neutron stars (extremely dense stars) are believed to be rotating at about 6 rev/s. If such a star has a radius of 15 km, what must be its minimum mass so that material on its surface remains in place during the rapid rotation?


    G=6.67*10-11m3 kg-1 s-2
    2. Relevant equations
    [tex]F_c{}=\frac{mv^{2}}{r}[/tex]
    [tex]F_g{}=\frac{GM_1{M_2{}}}{r^{2}}[/tex]

    3. The attempt at a solution
    30[tex]\pi[/tex]km*6rev/s=180[tex]\pi[/tex]km/s
    which gives the linear velocity of something on the surface of the neutron star.... but I'm clueless as to how to arrive at a mass of the star from it. I could the Centripetal acceleration but I'm not sure how that's related here. the only thing I can think of there is setting the centripetal acceleration equal to the gravitation acceleration which gives

    Gm/r2=v2/r
    m=v2r/G
    which yields something like 7.28635682 × 10^24(kg?)

    I'm just looking for advice on what I'm actually looking to do. I don't know what I should be looking for....
     
  2. jcsd
  3. Dec 2, 2009 #2

    ehild

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    Homework Helper
    Gold Member

    Your formula is correct, but check the calculation.

    ehild
     
  4. Dec 2, 2009 #3
    Thank you very much! I realized a dropped a "pi" at some point when I went back over it.
     
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