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Homework Help: Revolutions per second

  1. Oct 20, 2006 #1
    A sample of blood is placed in a centrifuge of radius 19.0 cm. The mass of a red blood cell is 3.0 10-16 kg, and the magnitude of the force acting on it as it settles out of the plasma is 4.0 10-11 N. At how many revolutions per second should the centrifuge be operated?

    I converted 19cm to .19m and then tried using F[c]=m*v(squared)/r but got the wrong answer. Is there a different formula I should be using or did i miss something else? Thank you!!
  2. jcsd
  3. Oct 20, 2006 #2

    Doc Al

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    Staff: Mentor

    Nothing wrong with that formula, but it gives you velocity--you need to convert to revolutions per second. (Hint: How far does the cell travel in one revolution?)
  4. Nov 1, 2007 #3
    SO would you multipy or divide how far the cell travels to the velocity. my problem conatins a centrifuge with velocity 114 meters per second but my circumference is .86 meters. WHere do i go from there im not too sure
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