1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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!

Share this great discussion with others via Reddit, Google+, Twitter, or Facebook