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Homework Help: Shaft speed of a motor at 80% efficiency

  1. Aug 6, 2011 #1
    1. The problem statement, all variables and given/known data

    A motor produces 1000kW of power, running at 1500rpm. What is the running speed if it runs at 80% power?

    2. Relevant equations

    None that I know of. You can find the torque by the below equation (but again, I don't know how to deal with the 80%)

    [tex] P = \frac{Tn}{9549} [/tex]
    where P is power (kW), T is torque (N.m), n is rotational speed in rpm.

    3. The attempt at a solution
    Is it just a proportion type thing?


    80% power means 0.8*1000 kW = 800 kW
    so then
    0.8*1500rpm = 1200 rpm ?
  2. jcsd
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