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Help With A Concept on Work: Should be Easy

  1. Oct 17, 2006 #1
    A 0.6 kg baseball is dropped out of a window that is 6.1 m above the ground. The ball is caught by a person whose hands are 1.5m above the ground.

    Questions
    What is the gravitational potential energy of the baseball, relative to the ground
    --When it is caught? (Is this -27.05 J ?)
    --when it is released? (Is this 0 J ?)

    just need some clarification...i already solved most of the problem so that im not struggling with! THANKS erryone
     
  2. jcsd
  3. Oct 17, 2006 #2

    berkeman

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    Staff: Mentor

    They say relative to the ground, so the PE gained by the ball is the work put into it to raise it from the ground to those two heights listed.
     
    Last edited: Oct 17, 2006
  4. Oct 17, 2006 #3
    I'm sorry...by your post im totally lost! All i need to know is if im right or wrong???? because if im right, then i know the conceptual approach to this kinda question...
     
  5. Oct 17, 2006 #4

    radou

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    Homework Helper

    While dealing with potential energy, you have to define the 'zero level' of potential energy. In your problem it is said 'relative to the ground', so this makes the ground your 'zero level'. Now, what is the definition of gravitational potential energy? Just plug in the two heights into the definition. The results you got don't look correct to me, btw.

    (The result you got for a) (only it's positive) is what is stated in the post above by berkeman - the work done by the force of gravity equals the change of potential energy, which is the difference in the potential energy between the position at the window and in the hands.)
     
    Last edited: Oct 17, 2006
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