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Help finding the work done given 3 different distances?

  1. Feb 13, 2014 #1
    1. The problem statement, all variables and given/known data

    a student lifts a book of 0.95 N to a height of 1.25 m. Then the student carries the book to a shelf at a distance of 8.0 m and places it at a height of 2.0 m. How much work did the student realize over the book?

    2. Relevant equations
    W = Fd


    3. The attempt at a solution

    .95 N * 1.25 m + .95 N * 2.0 m + .95 N * 8.0 m = 1.2 + 1.9 + 7.6 = 10.7 J

    Is this correct?
     
  2. jcsd
  3. Feb 13, 2014 #2
    No, since the only force in question here is weight force, and it doesn't do work at every displacement in the problem. It does for the lift from ground to 1.25m, but across the distance of 8.0m, does the force do any work? Think about the equation:
    $$W = Fdcos\theta$$
    Also, for the lift to 2.0m, you're misinterpreting the displacement. It says it's lifted to a height of 2.0m, not that the displacement is 2.0m. It starts at a height of 1.25m (from the first part), and then it's moved from there to 2.0m.
     
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