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Astronomic gravitation problems

  1. Jan 11, 2009 #1
    1. If the INternational space station has an orbital velocity of 9,000 m/s. find the time (in minutes) it takes to make one complete orbit.

    Relevant equations
    F = mv2/ R = m4[pi]2R / T2

    The attempt at a solution
    Is this the way to solve for T?
    Do I use earth mass and Earth R b/c that all the question says?

    2. A martian day is 1.03 earth days. At what altitude above Mars should a communications satelite be placed such that it always stay over the same spot above the surface of mars (answer in units of miles. 1000m = 0.62 miles

    Relevant equations
    F = ma = m4[pi]2R / T2
    a= GM/R2

    The attempt at a solution
    I know how to solve the problem but what kinda threw me off are the martian days given...
    Is T 354.36 days that is 365/1.03
    If it is, can i find "a" after the "m" cancel, than solve for R which is (mar's radius + mars altitude)

    3. find the lagrange Point between the sun and Jupiter. In between what two planets will you find this point?

    mass: 1.9x1027 kg

    mass: 1.99x1030

    distance betwwen sun and Jupiter: 778x106 km

    Relevant equations
    Im really not sure what is lagrange point equation, is it... GMsunmjupiter/ r
    r is the distance of Jupiter- sun ?
  2. jcsd
  3. Jan 11, 2009 #2


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    Homework Helper

    You have the velocity and and hence you have

    mv²/r = Gravitational force = GMm/r²

    This yields v² = GM/r

    What you don't know from that equation is r. But you want to calculate it, because v/r = ω

    and ω = 2πf = 2π/T or

    T = 2π/ω = 2πr/v
  4. Jan 11, 2009 #3


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