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Homework Help: ?Average speed?

  1. Apr 30, 2009 #1
    ???Average speed??

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

    As you have calculated, the average speed of an air molecule at room temperature is about 500 m/s. What is deltaR rms (root means squared) for an air molecule after five seconds?

    answer is in mm

    not even sure what mm is other than millimeters

    3. The attempt at a solution

    i though it would stay the same because the speed of a molecule does not depend on time though a medium does it??

    i tried 500 which was given in problem (units m/s)
    any help would be great
  2. jcsd
  3. Apr 30, 2009 #2
    Re: ???Average speed??

    I'm still trying to figure this out too.
    Look at pg 430 of your book.. the equation is there. I was told that we're supposed to use the mean path of nitrogen (N2) which is given on page 415.

    So it's:

    delta r rms = sqrt(v*d)*sqrt(t)

    d= mean path of N2 (7e-8m) given on page 415.
    Last edited: Apr 30, 2009
  4. Dec 10, 2009 #3
    Re: ???Average speed??

    then just multiply by a thousand since it is in meters and they want it in mm.. for all u phys 172 ppl out there searchin for this question
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