A 78.0 kg man stands on a spring scale in an elevator. Starting from rest, the e

Question

A 78.0 kg man stands on a spring scale in an elevator. Starting from rest, the elevator ascends, attaining its maximum speed of 1.61 m/s in 1.10 s. It travels with this constant speed for the next 5.00 s. The elevator then undergoes a uniform acceleration in the negative y direction for 1.60 s and comes to rest.

(a) What does the spring scale register before the elevator starts to move?
________ N

(b) What does it register during the first 1.10 s?
________ N

(c) What does it register while the elevator is traveling at constant speed?
________ N

(d) What does it register during the time it is slowing down?
________ N

Explanation / Answer

a) F = ma = 78*9.81 = 765.18N

b) a = dv/dt = 1.16/1.10 = 1.05m/s^2
F = F_a + ma = 765.18+78*1.05 = 847.434N

c) 765.18N

d) a = dv/dt = -1.16/1.6 = -0.725 m/s^2
F = F_a + ma = 765.18+78*-0.725 = 708.63N

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