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Homework Help: RMS velocity of air

  1. Jul 5, 2008 #1
    1. The problem statement, all variables and given/known data
    If the air pressure is 72 cm-Hg (as measured with a barometer), the velocity of sound is 344.7013 m/s and the temperature is 22.6 C calculate the Vrms.

    2. Relevant equations

    velocity = Vrms*sqrt[(1.40*n*Na*m)/(3*density*Vol)]

    3. The attempt at a solution

    I am under the impression that the Nam cancels out the density*volume, but I'm not getting the right answer. I'm really having trouble assigning values for all the parts of the equation.

    Thanks in advance.
    1. The problem statement, all variables and given/known data

    2. Relevant equations

    3. The attempt at a solution
  2. jcsd
  3. Jul 5, 2008 #2


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    Homework Helper

    If the quantities are what I think they are***, then n*Na*m would cancel density*volume. This will leave an equation with two quantities, "velocity" and "Vrms". I know what Vrms is, but have know idea what "velocity" refers to in this equation.

    Hint: can you find a different equation in your textbook, one that involves both Vrms and Temperature?

    *** p.s. correct me if I'm wrong, but I believe that:
    n is the number of moles of air molecules
    Na is Avagadro's number, 6.02 x 10^23
    m is the mass of a single molecule.
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