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Homework Help: Basic Orbit Satalite Questions Please help!

  1. Nov 26, 2007 #1
    1. The problem statement, all variables and given/known data

    The polar-orbiting environmental satellites (POES) and some military satallites orbit at a much lower level in order to obtain more detailed information. POES complete an earth orbit 14.1 times per day. What are the orbital speed and the altitude of POES?

    T = 1.7 h
    G = 6.67x10^-11
    M earth = 5.98x10 ^24

    2. Relevant equations

    The international space station orbits at an altitude of approximately 226km. What is its orbital speed and period?

    3. The attempt at a solution

    What i tried to do was,

    R^3 = (G)(M Earth)
    T^2 _____4π^2
  2. jcsd
  3. Nov 26, 2007 #2
    Somebody please help me ! :(
  4. Nov 26, 2007 #3

    D H

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    Staff Emeritus
    Science Advisor

    You have units for the orbital period, why not for G and the mass of the Earth? Those things have units too, and unless you apply them consistently you will get the wrong answer. You used the values [itex]G=6.67*10^{-11}\mathrm{m}^3/\mathrm{kg}/\mathrm{s}^2[/itex] and [itex]M_{\oplus}=5.98*10^{24} \mathrm{kg}[/itex] in conjunction with time in hours and distance in kilometers.
  5. Nov 26, 2007 #4

    So how do i do the question?
  6. Nov 26, 2007 #5

    D H

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    Staff Emeritus
    Science Advisor

    Make sure you use consistent units throughout. That value of G is in m3/kg/s2. If you want to use that particular value, you had better represent lengths in meters, not kilometers, and time in seconds, not hours.
  7. Nov 26, 2007 #6
    Ooo.. Thanks man :)

    But how do i use the equasion when they only give that much information, i am lost :( But i do understand your point.
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