A 83-kg man stands on a springscale in an elevator. Starting from rest, the elev

Question

A 83-kg man stands on a springscale in an elevator. Starting from rest, the elevator ascends,attaining its maximum speed of 1.2 m/s in 0.93 s. The elevator travels with thisconstant speed for 5.0 s, undergoes auniform negative accelerationfor 1.8 s, and then comes torest. What does the spring scale register in each of the followingtime intervals? (a) before the elevator starts to move
N

(b) during the first 0.93 sof the elevator's ascent
N

(c) while the elevator is traveling at constant speed
N

(d) during the elevator's negative acceleration
N
(a) before the elevator starts to move
N

(b) during the first 0.93 sof the elevator's ascent
N

(c) while the elevator is traveling at constant speed
N

(d) during the elevator's negative acceleration
N

Explanation / Answer

a) F = ma = 83*9.81 = 814.23N b) a = dv/dt = 1.2/0.93 = 1.29 m/s^2 F = F_a + ma = 814.23 + 83*1.29 = 921.364N c) 814.263N d) a = dv/dt = -1.2/1.8 = -0.66 m/s^2 F = F_a + ma = 814.23 + 83*0.66 = 869.56N

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