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Homework Help: Centrifugal/Centripetal Acceleration

  1. Oct 1, 2006 #1
    This question is actually posted up, but not under a very descriptive title so I'm reposting it and hoping the admin will just close my other one... sorry. Anyway, here is my problem-

    #1) A typical lab centrifuge rotates at 4000rpm. Test tubes have to be placed into a centrifuge very carefully because of the very large accelerations. What is the acceleration at the end of a test tube that is 10cm from the axis of rotation in?

    What I've already done is find the circumference of the circle, multiplied that by how many revs in a minute the lab does, divide that by 60 to get it in how many revs it does per second, then plug it into the centripetal acceleration equation a=(v^2)/r.

    Known- 4000rpm, r=5cm

    4000rpm * (2pi(r=5)) = 1256.6m/min
    1256.6/60 = 20.94m/s
    a = ((v=20.94)^2)/(r=.05m) = 8772.98m/s^2

    Obviously, this isn't right; so what do I need to do?
  2. jcsd
  3. Oct 2, 2006 #2

    Andrew Mason

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    Science Advisor
    Homework Helper

    Why are you using 5 cm as the radius? Should it not be 10 cm?

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