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Finding gravitational potential energy

  1. Apr 28, 2009 #1
    1. The problem statement, all variables and given/known data
    The distance between the sixth and the eleventh floors of a building is 30.0m. The combined mass of the elevator and its contents is 1350 kg.

    a) find the gravitational potential energy of the elevator when it stops at the eighth floor, relative to the sixth floor.

    (the answer in the back of my textbook is : 1.5x10^5 J )

    2. Relevant equations
    now i am thinking E=mgh, but i am also thinking that i an going to need to do something about the work formula. i know that w=F"d, and when the force is acting in the opposite direction, you must use W=F"d cos 180'. but this might be totally irrelevant.


    3. The attempt at a solution
    with this equation i am getting: E=1350(9.81)(30) E=397305 J
     
  2. jcsd
  3. Apr 28, 2009 #2

    LowlyPion

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    Homework Helper

    The distance between the 6th and 11th is 30 meters.

    The distance between the 6th and 8th then is 12 meters isn't it?
     
  4. Apr 28, 2009 #3
    yeah, thanks. i feel like an idiot about the question now..
    forgot to consider that fact that the 30m was for the whole height and not for floor 6-8.
     
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