1. A 65.0 kg person stands on a scale in an elevator. (a) What does the scale re

Question

1. A 65.0 kg person stands on a scale in an elevator.

(a) What does the scale read (in kg) when the elevator is at rest?
kg
(b) What does it read when the elevator is climbing at a constant speed of 5.5 m/s?
kg
(c) What does it read when the elevator is falling at 5.5 m/s?
kg
(d) What does it read when the elevator is accelerating upward at 5.5 m/s2?
kg
(e) What does it read when the elevator is accelerating downward at 5.5 m/s2?
kg

2. An elevator in a tall building is allowed to reach a maximum speed of 3.7 m/s going down. What must the tension be in the cable to stop this elevator over a distance of 3.0 m if the elevator has a mass of 1300 kg including occupants?
N

Explanation / Answer

1)

a)

at constant speed acceleration a = 0

mg - N= ma

N = mg = 65*9.8 = 637 N

(b)

N - mg = 0

N = mg = 637 N

(c)

here speed v = 5.5 m/s is constant

acceleration = 0

mg - N = 0

N = mg = 637 N

(d)

N - mg = m*a

N - 637 = 65*5.5

N = 994.5 N

(e)

mg - N = ma

637 - N = 65*5.5

N = 279.5 N

+++++++++++++

(2)

acceleration a = -v^2/2y

T - mg = m*a

T - (1300*9.8) = 1300*3.7^2/(2*3)

T = 15706.17 N

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