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Homework Help: How many stars in our galaxy if they had the mass of our Sun.

  1. Feb 28, 2010 #1
    1. The problem statement, all variables and given/known data

    The Sun rotates about the center of the Milky Way Galaxy at a distance of about 3.00x10^4 light years from the center (1ly= 9.50x10^5 m). If it takes about 200 million years to make one rotation, estimate the mass of our galaxy. Assume the mass distribution of our galaxy is concentrated mostly in a central uniform sphere. If all the stars had about the same mass as our Sun, how many stars would there be in our galaxy?

    2. Relevant equations

    I have no clue, the most common equation I use is g=GM/r^2 and a=v^2/r.

    3. The attempt at a solution

    I do not know where to start.
  2. jcsd
  3. Feb 28, 2010 #2
    Treat the galaxy as if it was a planet that the sun was orbiting.
  4. Mar 1, 2010 #3

    Char. Limit

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    Gold Member

    Well, g is just gravitational acceleration, and is the a in a=v^2/r... but there's an equation missing.

    [tex]a=\frac{4 \pi^2 r}{T^2}[/tex]
  5. Mar 1, 2010 #4
    Okay, so I did T= 200,000,000 yrs = 6.31x10^15 s
    & R= 2.85x10^20

    a= 4(3.14)^2*(2.85x10^20)/(6.31x10^15s)
    a= 2.81x10^-10

    I doubt this is right since it is negative
  6. Mar 1, 2010 #5

    Char. Limit

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    No it's not... the exponent is negative, but the number is positive, just very small. And it should be small...
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