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Homework Help: How much time does it take to lift the piano?

  1. Oct 12, 2004 #1

    I thought I knew how to solve for this problem but alas I was wrong. I'm hoping someone will be able to point me in the right direction.

    Here's the problem: A 1.40x10^2 kg piano is being lifted at a steady speed from ground level straight up to an apartment 18.0m above the ground. The crane that is doing the lifting produces a steady power of 4.00x10^2 W. How much time does it take to lift the piano?

    So here's what I did:

    The equation for power is P = W/t.

    The equation for W (work done) is W = (Fcos0)s.

    I have P (at least this is my thinking here). P is 4.00x10^2 and I would need to find W and then I could solve for t.

    F = ma, however I don't know what my acceleration is. I calculated it with 9.80 but my answer was incorrect. So if all my original thinking in finding t is correct then all I really need help with is finding F.

    Any help provided will be greatly appreciated.
  2. jcsd
  3. Oct 12, 2004 #2


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    Homework Helper

    Stunner, that does not equal work.

    Conservation of Mechanical Energy
    [tex] \Delta K + \Delta \Omega = 0 [/tex]

    By the way, if the speed is steady(i suppose it means constant) what will be the change of kinetic energy?

    You could apply (Conservative System Work)

    [tex] W = -\Delta \Omega [/tex]


    Newton's 1st Law

    [tex] \sum_{i=1}^{n} \vec{F}_{i} = 0 \rightarrow \vec{v} = constant [/tex]

    You could use this to establish the force exerted to lift it is equal to the weight of the piano, in magnitude.
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