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如图所示,一轻质杠杆可绕O点转动,在杠杆的A点挂一重为60N的物体甲,在B端施加一个力F,已知OA:AB=1:2,为使杠杆水平平衡,作用在B端的力为____ N;保持拉力F始终与杠杆垂直,将杠杆缓慢提升一段距离,在提升过程中,拉力F将____(选填“变大、不变或变小”).

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20,变小

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