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Homework Help: Satellite Orbit

  1. Oct 9, 2008 #1


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    1.Sputnik I, the first artificial satellite to circle the planet (October 1957) had a mean orbital radius of 6957 km. Compute its period in seconds

    2. I am using the equation T^2 = R^3/C

    3. I converted 6957 km to AU's which equals 4.638 E-5. When I plug in the numbers, and convert it to seconds, I come up with 9.96 seconds. Am I using the correct formula?

    Thanks for your help.
  2. jcsd
  3. Oct 10, 2008 #2

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

    G = 6.67E-11 (metres-cubed per kilogram per second-squared)
    M = 5.98E24 (kilograms)
    r = 6.957E6 (metres)
    Last edited: Oct 10, 2008
  4. Oct 10, 2008 #3


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    Homework Helper

    Hi Rake-MC,

    The way I read the problem, I think the radius of the earth is included in the 6957km given. Does that sound right to you?
  5. Oct 10, 2008 #4
    Hmm it's a bit ambiguous, but thinking logically I would entirely agree that the radius of the Earth is included in the 6957km. Clearly I was thinking purely mathemtically and not realistically.
  6. Oct 10, 2008 #5


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    My professor told me to use formulas V=2 pi r/T and V^2 = GM/R, but my answer is still incorrect. Any suggestions?

  7. Oct 10, 2008 #6
    Using either:

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

    Or the formula your professor gave you will yield the same answer.

    It looks like it'll be approximately 90 minutes.
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