You are in charge of installing a small food-service elevator(called a dumbwaite

Question

You are in charge of installing a small food-service elevator(called a dumbwaiter in the food industry) in acampus cafeteria. The elevator is connected by a pulley system to amotor, as shown in the figure below. The motor raises and lowersthe dumbwaiter. The mass of the dumbwaiter is 34 kg. In operation, it moves at a speedof 0.32 m/s upward, withoutaccelerating (except for a brief initial period, which we canneglect, just after the motor is turned on). Electric motorstypically have an efficiency of 80%.If you purchase a motor with an efficiency of 80%, what minimum power rating should the motor have?Assume that the pulleys are frictionless.
?kW
?kW

Explanation / Answer

If the minimum power rating of the motor is P, then .8P isavailable. so .8P = force * speed = weight * speed = 34*9.8*.32 P = 34*9.8*.32/.8 W = .133 kW

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