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Root-mean-square velocity

  1. Nov 7, 2007 #1
    1. The problem statement, all variables and given/known data

    (Q) Hydrogen molecules have a mass of 2u and oxygen molecules have a mass of 32u, where u is defined as an atomic mass unit (u = 1.660540 \times 10^{-27}\; {\rm kg}). Compare a gas of hydrogen molecules to a gas of oxygen molecules.

    At what gas temperature T_rms would the root-mean-square (rms) speed of a hydrogen molecule be equal to that of an oxygen molecule in a gas at 300 K?
    State your answer numerically, in kelvins, to the nearest integer.

    2. Relevant equations

    v = sqrt(3kT/m) where k is Boltzmann's constant.

    3. The attempt at a solution

    Using the above equation gives that Temperature is 300/16 = 18.75K. I know that this is a crazy answer but please don't laugh:frown:

    What's wrong with my solution?
  2. jcsd
  3. Nov 7, 2007 #2


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    I'll promise not to laugh if you will tell me why 18.75 K is a "crazy answer"!
  4. Nov 7, 2007 #3

    Thats almost close to absolute 0 and when i fed the answer in, it said "not quite" which I rake to be a euphemism for "this is nonsense!!!!"
  5. Apr 22, 2011 #4
    the question requests the "the nearest integer" your result is correct, but I think the anwser should be 19
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