如图4-3-2所示的杆可绕O点转动,若保持杆处于图中所示的位置静止,

如图4-3-2所示的杆可绕O点转动,若保持杆处于图中所示的位置静止,可在A端分别施加力F1F2F3F4,其中最小的力是_______.

答案

解析:杆可绕O点转动,对杆的转动有影响的是重力G和拉力F,由平衡条件可知:

MF+MG=0,即F·l-G·

=0,d为杆的长度,l为力F的力臂.要使作用在杆上的拉力F最小,则需F的力臂最大,因为F3的力臂最大,所以F3最小.


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