15. A 750 kg elevator starts fromrest. It moves upward for 3.50 s withconstant a

Question

15. A 750 kg elevator starts fromrest. It moves upward for 3.50 s withconstant acceleration until it reaches its cruising speed, 1.75m/s.

(a) What is the average power of the elevatormotor during this period?
1 W

(b) How does this power compare with the motor power when theelevator moves at its cruising speed?
Pcruising = 2 W (a) What is the average power of the elevatormotor during this period?
1 W

(b) How does this power compare with the motor power when theelevator moves at its cruising speed?
Pcruising = 2 W

Explanation / Answer

mass m = 750 kg Initial velocity u = 0 time t= 3.5 s cruing speed v = 1.75 m / s (a). the average power of the elevator motor during thisperiod = work / time                                                                                              = [ ( 1/ 2) m [ v^2 - u ^ 2 ] ] / t                                                                                              = 328.125 watt (b). the motor power when the elevator moves at its cruisingspeed = mg v                                                                                                     = 12862.5 watt

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