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Work done by motor with pulley wheel on spindle.

  1. Feb 20, 2012 #1
    I need to calculate the work done by an electric motor when it has a pulley wheel on the end but nothing on the pulley wheel. I know work done = force x distance. And of course force = mass x acceleration. But I cannot for the life of me think of how I am going to work out the acceleration? or the distance. Normally the distance is the distance of the object being pulled by the motor..but my motor isn't pulling anything over a distance.

    How do i get the acceleration for F and how do i get the distance?
    Thanks
     
  2. jcsd
  3. Feb 20, 2012 #2

    OldEngr63

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    Gold Member

    If there is a pulley on the motor, but no belt on the pulley, the motor is doing no useful work at all. The only work being done by the motor is overcoming internal friction in its own bearings, windage on the rotor, the pulley, etc.

    Now all of those statements in the previous paragraph assume that the motor is running in steady state, that is, at constant speed. If the motor is starting up, this is not true. The motor is doing work to accelerate the rotor (internal mass) and the pulley (external mass) and the shaft (partly internal, partly external mass). During start up, there is a definite acceleration involved, but this goes to zero after the steady state is reached.

    So, the question is, what case do you have?
     
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