The dumbwaiter d and its load have a combined weight of 600 lb, while the counterweight c weighs 800 lb. determine the power delivered by the electric motor m when the dumbwaiter (a) is moving up at a constant speed of 8 ft/s, (b) has an instantaneous velocity of 8 ft/s and an acceleration of 2.5 ft/s2, both directed upward

a) 2.91 hp

b) 3.81 hp

Explanation:

As we cans ee in the diagram given below force F has same direction as velocity , The power is equivalent to

A) Uniform motion

As both bodies are in equilibrium,therefore we have following relation

By free body for C:

2T - 800 = 0

T = 400 lb

By free body for D

F + T - 600 lb = 0

F = 600 - T

  = 600 - 400 = 200 lb

2)

we have

from equation of motion

by free body diagram C

F = ma

T = 384.5 lb

by free body diagram of D

F = ma

F =262.1 lb

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