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Homework Help: Question on binary stars & binary stars

  1. Aug 17, 2003 #1
    What a great forum, so many interesting things

    I am facing a problem with the working out for my last question in my practice paper, for my mid-year examinations.

    i dont know how to write the notation here, so i have just attatched a screenshot, i hope u dont mind.

    i just have to derive it. The hint says, use Kepler's third Law and that it is a description of the orbits of binary stars around their common centre of mass.

    Thank You.:smile:

    Attached Files:

  2. jcsd
  3. Aug 17, 2003 #2

    Sorry about the name of the thread, I dont know where the extra, "& binary stars" came from.

    Also, where is the picture? I uploaded it.

    I just read Tom's post at the start so i will write up what I have. Its all on a piece of a paper:

    mA = mass of star A
    mB = mass of star B

    Keplers third law,
    r^3/T^2 = GM/4(pi^2)

    Would it be sufficient to say that since in a binary system, they would robit according to Keplers third Law,

    mA + mB = r^3/T^2......(1)

    The text states formula (1) only, without any explanations.

    Even from here if I try to prove that,

    mA + mB = 4(pi^2)(r^3)/G(T^2)

    It doesnt work out.

    As you can probably see, i am a bit confused. Sorry about the messy-ness.
    Last edited by a moderator: Aug 17, 2003
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