a 800kg elevator starts from rest. It moves upwaed for 5s withconstant accelerat

Question

a 800kg elevator starts from rest. It moves upwaed for 5s withconstant acceleration until it reaches its cruising speed,1.75m/s. 1. what is the average power of the elevator motor during thisperiod? 2. how does this power compare with the motor power when theelevator moves at its cruising speed? P cruising =_____W a 800kg elevator starts from rest. It moves upwaed for 5s withconstant acceleration until it reaches its cruising speed,1.75m/s. 1. what is the average power of the elevator motor during thisperiod? 2. how does this power compare with the motor power when theelevator moves at its cruising speed? P cruising =_____W

Explanation / Answer

a) F - mg = ma F = m(a+g) a = v/t F = m((v/t) + g) W = Fx average speed: v/2, x = vt/2 W = (v/t + g)(mvt/2) W = 1/2mv^2 + mg(vt/ 2) P = mv^2/2t + mgv/2 P = (800x 1.75^2 / (2(5))) + (800x9.8x1.75 / 2) P = 7105 W b) P crusing = mgv =(800 x 9.8 x 1.75 ) = 13720 W To compare: Ratio of P/Pc = 7105/12720 = .516

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