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Homework Help: Calculate Molecular Mass

  1. Jan 24, 2012 #1
    1. The problem statement, all variables and given/known data

    I need to calculate the mas of a molecule of an unknown gas in the atmosphere from the values:

    T = 500 K
    mass of the planet = 1.5 × 1024 kg
    radius is 3.0 × 106 m
    universal constant of gravitation, G = 6.67 × 10^−11 N m^2 kg^−2
    P at ground level = 2.0 × 10^7 Pa
    P at 50km altitude = 2.0 × 10^5 Pa

    2. Relevant equations


    but I can't find an equation involving G :(

    3. The attempt at a solution

    I am completely stuck, if I can get ahint where to start I'll have a go and see if I get anywhere.
  2. jcsd
  3. Jan 24, 2012 #2
    On Earth

    F = mg = GmM/R^2 so g = GM/R^2
  4. Jan 25, 2012 #3
    Right, I've got so far as calculating g now and have calculated a very low value for g compared to earth which is consistent with having a smaller mass than earth. I've also worked out an equation for m by rearranging λ=kT/mg ut the value doesn't match that of the two gases it could be by a factor of 10^3.
    Last edited: Jan 25, 2012
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