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

Question

You are in charge of installing a small food-service elevator (called a dumbwaiter in the food industry) in a campus cafeteria. The elevator is connected by a pulley system to a motor, as shown in the figure below. The motor raises and lowers the dumbwaiter. The mass of the dumbwaiter is 38 kg. In operation, it moves at a speed of 0.37 m/s upward, without accelerating (except for a brief initial period, which we can neglect, just after the motor is turned on). Electric motors typically have an efficiency of 81%. If you purchase a motor with an efficiency of 81%, what minimum power rating should the motor have? Assume that the pulleys are frictionless.
 kW

You are in charge of installing a small food-service elevator (called a dumbwaiter in the food industry) in a campus cafeteria. The elevator is connected by a pulley system to a motor, as shown in the figure below. The motor raises and lowers the dumbwaiter. The mass of the dumbwaiter is 38 kg. In operation, it moves at a speed of 0.37 m/s upward, without accelerating (except for a brief initial period, which we can neglect, just after the motor is turned on). Electric motors typically have an efficiency of 81%. If you purchase a motor with an efficiency of 81%, what minimum power rating should the motor have? Assume that the pulleys are frictionless. kW

Explanation / Answer

power P = Force * velocity                = mg*velocity                = 38*9.8*0.37                = 137.778 W                = 0.13 KW

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