力學問題求解(物理)?

[匿名]

2016-09-14 10:21 am

1.一部重量為8000N的升降機以恆定速率2ms/-1上行。繞於鼓軸上的鋼索為上行的升降機提供向上的力,而鼓軸則以電動機驅動。鋼索另一端固定於鼓軸上的尾端。空氣阻力和鋼索的質量可略去不計。
a(1).計算電動機對上行升降機所輸出的機械功率。
a(2).電動機的總機械功率輸出為20kW。對抗活動組件之間摩擦的功率損失是多少?
b.現放鋼索另一端裝上7000N的平衡錘。平衡錘的移動方向跟升降機相反,而升降機同樣以2ms/-1上行。假設鋼索與鼓軸之間並沒滑移。
b(1).計算電動機在此情況下的總機械功率輸出。假設對抗活動組件之間摩擦的功率損失跟(a)的相同
b(2).指出裝設了平衡錘的好處

回答 (1)

天同

2016-09-14 12:25 pm

✔ 最佳答案

a(1) Mechanical power (機械功率) delivered to lift
= 8000 x 2 W = 16,000 W = 16 kW

a(2) Power lost by friction = (20 - 16) kW = 4 kW

b(1) Net force required from the motor
= (8000 - 7000) N = 1000 N
Hence, mechanical power needed by the lift to go up at 2 m/s
= 1000 x 2 W = 2,000 W = 2 kW

Total mechanical power output (總機械功率輸出) by the motor
= (2 + 4) kW = 6 kW

b(2) The installation of balance weight (平衡錘) leads to less power output from the motor. Hence, resulted in less electricity consumption and less cost in running the lift..

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