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【简答题】
螺旋千斤顶是一种常用的起重装置（如图所示），用手柄转动螺杆时，螺杆顶端的重物就随螺杆一起上升。若螺杆的直径为D，螺距为h，手柄末端到转轴的距离为l，要举起质量为M的重物时，至少要给手柄顶端多大的力？指出本题中为了省力应用了哪几种简单机械。
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参考答案：
参考解析：
刷刷题刷刷变学霸
举一反三
【单选题】In its early history, Chicago had floods frequently, especially in the spring, making the streets so muddy that people, horses, and carts got stuck. An old joke that was popular at the time went somet...
A.
horses were fairly useful in Chicago
B.
Chicago"s streets were extremely muddy
C.
Chicago was very dangerous in the spring
D.
the Chicago people were particularly humorous
【多选题】下列选项中，可以采用集群液压千斤顶整体提升吊装法的有（ ）。
A.
大型屋盖的吊装
B.
体育场馆钢屋架的整体滑移
C.
油罐的倒装
D.
电厂发电机组的安装
E.
大型电视塔钢桅杆天线整体提升