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Contact Force help

  1. Oct 8, 2006 #1
    A woman is straining to lift a large crate, without success. It is too heavy. We denote the forces on the crate as follows: P is the upward force being exerted on the crate by the person, C is the contact force on the crate by the floor, and W is the crate’s weight. How are the magnitudes of these forces related, while the person is trying unsuccessfully to lift the crate?

    a.P = C
    b.P + C > W
    c.P + C < W
    d.P + C = W

    Is it that P + C = W if in equilibrium? P + C - W = 0; P + C = W

  2. jcsd
  3. Oct 8, 2006 #2

    Chi Meson

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    You are correct. It is still equilibrium since the normal contact force will automatically be lessened if another force is applied upward. The moment P is slightly more than W, then C goes to zero, and the crate accelerates slightly to move off the floor.
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