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Torque, the mass that can be lifted, and speed it rises

  1. Oct 31, 2009 #1
    1. The problem statement, all variables and given/known data

    a. compute the torque developed by an industrial motor whose output is 225kW at an angular speed of 4000rpm.
    b. a drum with negligible mass and .4m diameter is attached to the motor shaft, and the power output of the motor is used to raise a weight hanging from a rope wrapped around the drum. how heavy a weight can the motor life at constant speed?
    c. at what constant speed will the weight rise?

    2. Relevant equations
    rpm x 2pi/60s = rad/s angular speed (w) = 418 rad/s
    1Kw = 3.6x10^6J
    Power = (torque)(angular speed)?
    V = Rw

    3. The attempt at a solution
    i changed the w from rpm to rad/s
    I converted kW to J and got 81x10^8J
    I'm not sure that's right, that seems really big to me.
    and if Power = (torque)(angular velocity) then i rearranged and solved for torque and got 19.4x10^6, which seems high to me
    I have no idea what to do with part B
    I know that tension in the rope equals the weight of the object tied to it.
  2. jcsd
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