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Homework Help: Calculate mass of the sun

  1. Nov 9, 2004 #1
    hey there, i am having trouble with what should be a really easy question!
    calculate the mass of the sun assuming that the earths orbit is circular
    and with a radius of 1.5 * 10^8 km

    i got the period of the earths orbit around the sun in seconds:

    then used the formula:

    T = ((4*Pi^2*r^3)/(G*M))^2

    rearranging in terms of M

    i change the radius of the orbit to metres instead of kilometres before putting
    it into the formula.

    but the answer i get is 1.9 * 10^30 kg
    and i think the answer should be in the order of 10^40 kg

    can anyone suggest where i might be going wrong?


  2. jcsd
  3. Nov 9, 2004 #2
    This is Kepler's Law

    [tex] T^2 = \frac{4 \pi^2}{GM} r^3 [/tex]

    rearranged into

    [tex] M = \frac{4 \pi^2}{GT^2} r^3 [/tex]

    now sub in and see what s wrong
  4. Nov 9, 2004 #3
    i see i wrote the formula wrong in my original post!
    i meant raised to the power of 1/2 at the very end.
    i am still getting 2 * 10^30 as my answer..
    this might be the correct answer and the question is just

  5. Nov 9, 2004 #4
    the question is not unrealistic, the mass of the sun is 1.99x10^30 kg the answer of the book of 10^40 is wrong (or you're looking at the wrong question)
  6. Nov 9, 2004 #5
    ahh thank you! i found the value from a search on google :-S
    it didnt even cross my mind that the value was wrong.

    thank you very much!

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