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Power and mass

  1. Aug 1, 2013 #1
    1. The problem statement, all variables and given/known data

    A motor,rated 100W,runs from a source voltage 120V.If 2A of current flows through it then calculate the mass of water pumped by it to a height of 10m in 5 seconds.

    2. Relevant equations

    P=IV
    P=E/t
    E=mgh

    3. The attempt at a solution
    P=IV
    P=mgh/t
    mgh/t=IV
    m=IVt/gh
    m=(2)(120)(5)/(9.8)(10)
    m=12.24kg.

    Is my solution correct and does this question make correct sense?
    Thanks.
     
  2. jcsd
  3. Aug 1, 2013 #2

    PeterO

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    Homework Helper

    P = V.I formula gives P = 120 x 2 = 240W, yet the motor is rated at 100W.
    Could it be that the engine is not perfectly efficient, the rating means a power output is 100W?
    The rating of a motor is usually the maximum output of that motor, so the answer might be much smaller, as in (100)(5)/(9.8)(10)
     
  4. Aug 1, 2013 #3
    No.its 240W.i asked my teacher and he said there was a typo in the question.
     
  5. Aug 1, 2013 #4

    PeterO

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    Homework Helper

    You should tell about the typo then!!

    Did he say the typo was that the motor was rated at 1000 W?
     
  6. Aug 1, 2013 #5
    Yup.its actually 240W.i have an older edition of the textbook and its corrected in the newer edition.my teacher checked and told me.
     
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