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Homework Help: Dust Equipartitions

  1. Dec 10, 2008 #1
    calculate the rms (root-mean-square) speed v_rms of these particles, assuming them to be spheres of diameter 5 \; \mu {\rm m} and density 2 \; {\rm g}/{\rm cm}^3 = 2000 \; {\rm kg}/{\rm m^3}. The mass of such a dust particle is 1.31 \times 10^{-13} \; \rm kg.
    Express your answer in millimeters per second to one decimal place only.

    So I found out from the previous problem that the equation to use is:

    v_rms =\sqrt{\left(\frac{\left(3k_{B}T\right)}{\left({\rho}\left(\frac{4}{3}\right){\pi}\left(\frac{d}{2}\right)^{3}\right)}\right)}

    And after I plugged everything into the equation, I got 3*10^13 mm/s as the answer.

    I am pretty sure that I converted everything to the right units, I double checked my work a few times already, I don't know what I 've done wrong.

    Please help?
  2. jcsd
  3. Dec 12, 2008 #2


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    Hi doggieslover! :smile:

    Since nobody's replied in over 36 hours, maybe they can't read it … so here's a translation :rolleyes:
  4. Dec 12, 2008 #3


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    What did you use for T, and why? Do you understand the meaning of this formula?
  5. Dec 13, 2008 #4
    T = 290K, it was given in a previous problem, I forgot to incorporate it in here.

    I solved it already, the answer is .3mm/s, I probably just converted something wrong.
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