A 65-kg man stands on a spring scale in an elevator. Starting from rest, the ele

Question

A 65-kg man stands on a spring scale in an elevator. Starting from rest, the elevator ascends, attaining its maximum speed of 1.2 m/s in 0.79 s. The elevator travels with this constant speed for 5.0 s, undergoes a uniform negative acceleration for 1.4 s, and then comes to rest. (a) What does the spring scale register before the elevator starts to move? N (b) What does the spring scale register during the first 0.79 s of the elevator's ascent? N (c) What does the spring scale register while the elevator is traveling at constant speed? N (d) What does the spring scale register during the elevator's negative acceleration? N

Explanation / Answer

a) man of mass 65kg starting form rest so gravitaltional force will be there so g=10m/s2

Fa= mg = 65x10=650N

b) accelaration a = dv/dt =1.518m/s
F = Fa + ma = 650+65x1.518 = 748.67N

c) 650N

d) a = dv/dt = -1.2/1.4 = -0.8.57 m/s2 because it is nagative accelaration
F = Fa + ma = 650+65x-0.857 = (650-55.705)N

F=594.295N

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