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Minimum work physics problem

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

    What is the minimum work done when a 65 kg student climbs an 8.0 m-high stairway in 12 s?




    3. The attempt at a solution
    v=d/t
    v=8/12
    v=2/3

    v = v2+v1 over 2
    2/3 = v2+0 over 2
    v2 = 2x[2/3]
    v2=4/3

    w=deltaEk
    w=.5x65x[4/3]^2 - .5x65x0
    w = 57 j ?

    answer is 5100 j
     
  2. jcsd
  3. Apr 19, 2009 #2

    fluidistic

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    Gold Member

    Re: work.

    Hint :work is force times distance. So the time taken does not matter at all.
     
  4. Apr 19, 2009 #3
    Re: work.

    Edit I get it, trick question lol.
    thank you.
     
  5. Apr 19, 2009 #4

    fluidistic

    User Avatar
    Gold Member

    Re: work.

    It seems you got the answer!
    The minimum work needed would be done by a force acting upward, in the opposite direction of the weight. Its magnitude would have to be greater than the weight, so >65 kg*9.8m/s^2 as you did.
    You wrote w=fd, where w is the work, f is the force and d is the distance. Then you said that the formula doesn't have a distance?
    Well you've done it :)
     
  6. Apr 19, 2009 #5
    Re: work.

    haha, i know what I typed wasnt actually what I did.
     
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