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Homework Help: Centrifuge HW Problem

  1. Sep 28, 2005 #1
    A sample of blood is placed in a centrifuge of radius 16.0 cm. The mass of a red blood cell is 3.0e-16 kg, and the magnitude of the force acting on it as it settles out of the plasma is 4.0e-11 N. At how many revolutions per second should the centrifuge be operated?

    I can figure out the velocity... but the answer needs to be in revolutions per second. Would I just divide the velocity by the circumference of the centrifuge??
     
    Last edited: Sep 28, 2005
  2. jcsd
  3. Sep 28, 2005 #2

    Doc Al

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    Staff: Mentor

    That's correct.
     
  4. Sep 28, 2005 #3
    Ok, I figured out the problem using F=m(v^2/r). I got the right answer when I kept the mass in kg and solved for v. How could that be right if the answer had to be in rev/s? I don't get it...
     
  5. Sep 28, 2005 #4

    Doc Al

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    Staff: Mentor

    Calculate the circumference and you'll get it. :wink:
     
  6. Sep 28, 2005 #5
    Lol

    Soooo sneaky... hehe
     
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