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Homework Help: Force exerted on a block

  1. Feb 1, 2010 #1
    1. The problem statement, all variables and given/known data

    During World War II, 16 huge wooden hangers were built for the U.S. Navy airships. The hangers were over 300 m long and had a maximum height of 52.0 m Imagine a 40.0 kg block being lifted by a winch from the ground to the top of the hanger's ceiling. If the winch does 2.08 x 10^4 J of work in lifting the block, what force is exerted on the block?

    2. Relevant equations

    KE = 1/2 mv^2
    Net Work = deltaKE

    3. The attempt at a solution

    Could someone please explain to me, in detail, what to do here?
    if you can, much appreciated!
    Thank You
     
  2. jcsd
  3. Feb 2, 2010 #2

    tiny-tim

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    welcome to PF!

    well, hello duckywucky! welcome to pf! :wink:

    (have a delta: ∆ and try using the X2 tag just above the Reply box :smile:)
    No, ∆KE = 0 (it's not launching the thing, is it? :rolleyes: :smile:)

    Try ∆PE. :smile:
     
  4. Feb 2, 2010 #3
    So does that mean I would do (40.0)(9.81)(2.08 x10^4)?
    I came up with 814.192 but in scientific notation, it would be: 8.16 x 10^6 J?
     
  5. Feb 2, 2010 #4

    tiny-tim

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    why?? :confused: explain in words.
     
  6. Feb 2, 2010 #5
    I have no idea to be honest. Our class hasn't covered potential energy yet so i don't know what the formula is for it. XD
     
  7. Feb 2, 2010 #6

    tiny-tim

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    hmm … thought so! :rolleyes:

    ok, so presumably the only equation you know is work done = force times distance.

    in that case, what figures have you been given that you can put into that equation? :smile:
     
  8. Feb 2, 2010 #7
    Work done is 2.08 x 10^4.
    You're looking for Force, but i'm not sure the distance...maybe 300 m?
     
  9. Feb 2, 2010 #8

    tiny-tim

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    Read the question

    "lifted by a winch from the ground to the top of the hanger's ceiling" …

    that's not 300 m.
     
  10. Feb 2, 2010 #9
    Work done is 2.08.
    Force of gravity is 9.81
    And the mass of the block is 40.0 kg.
     
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