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Homework Help: Find the size of Driving couple, if given the power?

  1. Mar 9, 2012 #1
    1. The problem statement, all variables and given/known data
    Not really HW, just revision.

    A shaft rotating at 3000 revolutions per minute is transmitting power of 10000 watts. find the size of the driving couple.

    2. Relevant equations
    Total wrk done by couple = 2.F.r.θ
    Work = Torque . θ ( angle of rotation )
    Power = work done / time

    3. The attempt at a solution

    60 seconds = 3000 revolutions
    1 second = ?

    Ans came to 50

    Using ω = 2∏f resulted in ω = 100∏

    Power = (Torque . θ)/t where θ/t = ω

    Subject of the formula gave me 9.54 as an answer. When it should be 32Nm

    What have I done wrong?
  2. jcsd
  3. Mar 9, 2012 #2


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    Science Advisor
    Homework Helper

    welcome to pf!

    hi alec433lawrid! welcome to pf! :smile:
    i get 32

    how did you get 9.54 ?​
  4. Mar 9, 2012 #3
    Re: welcome to pf!

    Oh wow!, I am such a noob!

    Sorry for wasting your time.

    I did have the correct answer. ie my reasoning was correct. My calculator skills on the other hand let me down :(

    I did 10000 / 100∏
    when i should have done 10000 / (100 * ∏ )

    It was a stupid mistake....
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