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Homework Help: Work Against Force

  1. Oct 23, 2008 #1
    1. The problem statement, all variables and given/known data
    You cannot pick up a piano and put it on a moving truck because you (choose one)
    a)cannot exert enough force to life the piano
    b)cannot perform enough work to lift the piano
    c)can neither exert enough force nor perform enough work to lift the piano

    2. Relevant equations

    3. The attempt at a solution
    I think it's c because if you could do either a or b, you would be able to life the piano.
    Last edited: Oct 23, 2008
  2. jcsd
  3. Oct 23, 2008 #2
    You could perform enough work to lift the piano. Imagine connecting it to an intricate system of pulleys such that you could pull lightly on the rope for a very long distance of rope and lift the piano. It'd be the same amount of work (W=F*d). Think you could do it?
  4. Oct 23, 2008 #3
    I think the question is saying without any other devices, why can't you life the piano?
  5. Oct 23, 2008 #4
    Ah, but the amount of work done is the same no matter how you lift it -- that was my point.
  6. Oct 23, 2008 #5
    1. i think the answer is a.
    2. When the piano is lifted, its gravitational potential energy will increase. The piano gets this energy if you do work on it. But to do the work, you need to exert a force equal to its weight on the piano and then to move it some distance upwards.
    3. Our body can't produce that kind of large force, thus it is not possible.
  7. Oct 23, 2008 #6
    But without any other helping objects, our body can't do the work required, right?

    BTW, do you think the answer is a then?
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