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Work on object lifted in a gravational field

  1. Mar 6, 2008 #1
    A 1.1 kg book is lying on a 0.80-m-high table. You pick it up and place it on a bookshelf 2.17 m above the floor.

    How much work does gravity do on the book?
    How much work does your hand do on the book?

    W=mgh

    (1.1 kg)(9.8 m/s^2)(0.8m)=8.6

    The answers that I am getting are wrong
    Please help
     
  2. jcsd
  3. Mar 6, 2008 #2
    The book is initially on the table and then its moved to the shelf. So it moved (2.17-0.8) m
    Also, work done by gravity will be negative.
     
  4. Mar 6, 2008 #3
    Help

    Now I have another problem

    A 10 g particle is moving to the left at 29 m/s. How much net work must be done on the particle to cause it to move to the right at 47 m/s?

    W=mg[tex]\Delta[/tex]r

    I got 1.7. I don't think I am doing this right.
     
  5. Mar 6, 2008 #4

    tiny-tim

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    Show us how you got 1.7 :confused:

    (btw, if you type alt-j, it give you ∆ without having to tex! :smile:)
     
  6. Mar 6, 2008 #5
    (.01kg)(9.8m/s^2)(47 m/s - 29m/s) = 1.7

    I have a feeling that i am completely doing it wrong
     
  7. Mar 6, 2008 #6
    Got it

    Forget about this question. I got it
     
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