An 80-kg person steps into a stationary elevator on the top floor of a building.

Question

An 80-kg person steps into a stationary elevator on the top floor of a building. The person steps on a scale. The person presses the button for the bottom floor. The elevator speeds up to 6.0 m/s in 3.0 seconds.

c) Calculate the reading (in newtons) of the scale while the elevator maintains its speed, assuming the acceleration, if any, is uniform.

Next, the elevator slows to rest in 2.5 seconds.

d) Calculate the reading (in newtons) of the scale while the elevator slows down, assuming the acceleration, if any, is uniform.

Next, the elevator remains at rest for 4.0 seconds.

e) Calculate the reading (in newtons) of the scale while the elevator is stationary, assuming the acceleration, if any, is uniform.

I already figured out a) and b) but I'm having a hard time with c) - e)

Explanation / Answer

c) reading (in newtons) of the scale = m(g-a) = 80(10-2)

acceleration is 2 as rate of change of v = 6/3 = 2

so reading = 640 N

d)elevator slows to rest in 2.5 seconds so a = -6/2.5 = -2.4 m /s2

so reading now = 80(10-(-2.4)) = 992 N

e)the reading is the weight of the man = mg = 800 N

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