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Force diagram

  1. Feb 28, 2014 #1
    The vertical motion of an elevator is recorded and a Position vs Time plot is generated. The plot is shown in the image attached.

    1. Construct a scale drawing of the associated Velocity vs Time plot complete with axis labels.

    2. Calculate the average acceleration for the time interval t =8.0s to t = 10s.

    3. Sketch a force diagram of an elevator occupant with a mass of 70 kg during the time interval t =8.0s to t = 10s.

    4. Calculate the Normal force F N of the occupant using the acceleration you calculated in part 2

    Can somebody please tell me where I went wrong? Thanks!!

    Mt attempt:
    1. Velocity during 0 to 10 = 14 m / 10 s = 1.4 m/s
    Velocity during 10 to 19 = 0 m/s
    Velocity during 19 to 25 = -14 m /6 s = - 2.33 m/s

    2. a = delta v/delta t = 0 - 1.4 m/s/2 s = -0.7 m/s^2

    3. I have no clue. How do you figure this one out?

    4. Fn = 70 kg * -2.33 m/s^2 = -163.10 N

    Attached Files:

  2. jcsd
  3. Feb 28, 2014 #2


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    Gold Member

    3. you know the mass and the acceleration, so you know the force for the asked interval.
  4. Feb 28, 2014 #3
    Yea but apparently my answers to other questions are also wrong. I don't know what's the problem. And 3 is asking for a force sketch.
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