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Homework Help: Units - is this m/s or mm/s?

  1. Jan 21, 2009 #1
    Units -- is this m/s or mm/s?

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

    2. Relevant equations


    3. The attempt at a solution

    I've solved a problem as follows

    (pi * 10.0mm²)(0.200m/s)=(pi * 2.50mm²)(v2)
    3.20 xx/s = v2

    I am pretty sure it's in m/s, but having the radii in millimeters is confusing me. I would convert all to meters, but I am required to solve using 3sf, so I would lose accuracy on the 2.50mm.

    Am I correct in thinking the answer is in m/s?
  2. jcsd
  3. Jan 21, 2009 #2
    Re: Units -- is this m/s or mm/s?

    You can never lose accuracy by converting millimeters to meters, and vice-versa, since the two are separated by a constant. You have the right idea - turn everything into meters, and if you want, you can turn the end product back into millimeters.
  4. Jan 21, 2009 #3
    Re: Units -- is this m/s or mm/s?

    Heh, I converted 2.50mm to 0.025m and, for whatever reason, I got the idea in my head that I would have to reduce it to 0.020m to still have 3sf. I went back and did a bit of review on sf and figured it out :p

    Thanks for the response!
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