In Example 5.8, we investigated the apparent weight of a fish in an elevator. No

Question

In Example 5.8, we investigated the apparent weight of a fish in an elevator. Now consider a 72.0-kg man standing on a spring scale in an elevator. Starting from rest, the elevator ascends, attaining its maximum speed of 1.20 m/s in 0.800 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 1.50 s and comes to rest. What does the spring scale register (a) before the elevator starts to move, (b) during the first 0.800 s, (c) while the elevator is traveling at constant speed, and (d) during the time interval it is slowing down?

Explanation / Answer

a W = mg W = 72 x 9.8 = 706 N b. a = v/t = 1.2/0.8 = 1.5m/s2 W - mg = ma W = m (g + a) = 814 N c. W - mg = ma W - mg = 0 W = mg W = 72 x 9.8 = 706 N d. a = v/t = 1.2/1.5 = 0.8m/s2 W - mg = - ma W = m (g - a) = 648 N

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