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elijahproctor36
18.02.2020 •
Physics
• Zach, whose mass is 80 kg, is in an elevator descending at 10 m/s. The elevator takes 3.0 s to brake to a stop at the first floor. What is Zach’s weight before the elevator starts braking? What is Zach’s weight while the elevator is braking?
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Ответ:
Explanation:
mass, m = 8 kg
initial velocity, u = 10 m/s
time, t = 3 s
final velocity, v = 0 m/s
Let the acceleration is a
use first equation of motion
v = u + at
0 = 10 - a x 3
a = 3.33 m/s² downward
As the elevator is moving with constant velocity so the weight is the true weight = m x g = 80 x 9.8 = 784 N
Now the elevator is moving down with an acceleration is 3.33 m/s², let the weight is R.
Use Newton's second law
mg - R = ma
R = m ( g - a)
R = 80 ( 9.8 - 3.33)
R = 517.6 N
Ответ: