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Accelerating lift

  1. Apr 27, 2005 #1
    [​IMG]

    A painter in a crate hangs alongside a building.

    When the painter, who weighs 1000 N, pulls on the rope, the force he exerts on the floor of the crate is 450 N. If the crate weighs 250 N, find the acceleration. (ans=1.96 m/s²)


    Lift accelerates upwards, because man is pulling down.

    hence,
    N (upwards) - mg (downwards) = ma (upwards)

    Is it right?

    Question:
    for mg and ma, do I need to take into account the mass of the crate?
     
  2. jcsd
  3. Apr 27, 2005 #2

    HallsofIvy

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    Staff Emeritus
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    "Lift accelerates upwards, because man is pulling down."

    Are you sure of that? Remember, he is in the crate himself! He has to lift both himself and the crate. What is the total weight he is trying to lift? Once you have figured out the net force (weight downward, rope pulling up), you need to find the mass corresponding to that total weight in order to find acceleration.
     
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