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电梯由一个起重间与一个配重组成。它们分别系在一根绕过定滑轮的钢缆的两端(图4-1)。起重间(包括负载)的质量 ,配重的质量 。此电梯由和定滑轮同轴的电动机所驱动。假定起重间由底层从静止开始加速上升,加速度 。(1)这时滑轮两侧钢缆中的拉力各是多少?(2)加速时间 ,在此时间内电动机所做功是多少(忽略滑轮与钢缆的质量)?(3)在加速 以后,起重间匀速上升。求它再上升 的过程中,电动机又做了多少功?
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反馈参考答案：
举一反三
【单选题】Students from a wide range of countries attend a professional exam: A questionnaire is sent to a selected number of students at the end of the exam which should be completed compulsorily. The samples ...
A.
Multi-stage
B.
Stratified
C.
Cluster
D.
Systematic
【单选题】Samples are provided by the buyer as the quality standard for the goods. In order to avoid future disputes over the quality of the goods, the seller usually first duplicates the samples and then sends...
A.
duplicate sample
B.
original sample
C.
counter sample
D.
sealed sample
【单选题】When each data value in one sample is matched with a corresponding data value in another sample, the samples are known as
A.
corresponding samples
B.
matched samples
C.
independent samples
D.
None of these alternatives is correct.
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