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Homework Help: Can any one help with this Fluid mechanics question please?

  1. Jan 8, 2013 #1
    1. The problem statement, all variables and given/known data
    A shaft of diameter 74.9mm rotates at 1400rpm in a bearing which is of diameter 75.03 mm and 75mm in length. The annular space between the shaft and the bearing is filled with oil of viscosity 0.096 kg/ms.By assuming a uniform velocity gradient in the oil, determine the power required to overcome the viscous resistance in the bearing.

    2. Relevant equations

    Thats the equation i have been using, where l is the difference between the radius of the outer ring and inner ring (i.e. bearing and shaft)

    3. The attempt at a solution

    When i plug in the values i get:
    0.096* ((146.61*37.45*10^-3)/0.065*10^-3)*2∏*(37.45*10^-3)(75*10^-3)

    this gives 143.12N

    Presuming that this is all ok i then have no idea how to get to a power?
  2. jcsd
  3. Jan 8, 2013 #2


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    Staff Emeritus
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    Homework Helper

    How much torque would this force produce on the shaft when it is turning at 1400 rpm? Once you know the torque, you can find the power.
  4. Jan 8, 2013 #3
    Ah yeah thanks got the right answer :)
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