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一、知识准备我们已经学过,杠杆只受一个动力和一个阻力作用下的平衡条件是:动力×动力臂=阻力×阻力臂。如果杠杆受两
I. Knowledge Preparation We have learned that the balance condition under which a lever is subject to only one power and one resistance is: power x power arm = resistance x resistance arm. If the lever is subject to two