Force Diagram, Position vs Time Plot: Construct, Calculate, Sketch

[BrownBoi7]

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

 

[ChrisVer]

3. you know the mass and the acceleration, so you know the force for the asked interval.

 

[BrownBoi7]

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.