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Homework Help: Simple question about the power generated by an elevator motor

  1. Dec 19, 2009 #1
    1. The problem statement, all variables and given/known data

    The motor of an elevator generates 12000 Watts of power when moving the elevator at constant speed of 2 m/s.what is the mass of elevator in kg ...??

    There are 5 options for the answer.

    a) 500 Kg b) 400 Kg c) 300 Kg d) 240 Kg e) 200 Kg

    2. Relevant equations

    P = W/t

    3. The attempt at a solution

    I tried to solve it like this ..

    Power = Work / Time = Force * Displacement / Time = Force * Velocity = m*a*v

    So m = P / a*v

    where a is the gravitaional acceleration = 9.8 m/s2
    v is the constant speed = 2 m/s
    P is the power = 12,000 Watts

    I simply plugged in the numbers & got 612 Kg which is obviously wrong. Any help would be apprecitaed. Thanks
  2. jcsd
  3. Dec 19, 2009 #2
    It looks good to me, even if you use g=10m/s^2, the answer is 600 and not among the choices.
  4. Dec 19, 2009 #3
    thx for ur responding.

    So shall i take the nearest answer which is 500 Kg or what ..??
  5. Dec 19, 2009 #4
    Go ahead and answer 500, and take your work to the prof. Unless I'm missing something..the question will get kicked out.
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