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例1 如图1,水平放置的两根固定的光滑硬杆OA、OB之间的夹角为θ,在两杆上各套轻环P、Q,两环用轻绳相连,现用恒力F沿OB杆方向向右拉环Q,当两环稳定时,绳的拉力是多大? 分析 将题中各隐含条件转化为显性条件: (1)轻环→不计重力,光滑杆→不计摩擦. (2)环套在杆上→属于点与线接触,P、Q所受弹力方向与杆垂直. (3)两环稳定→静止状态→F合=0. 综上所述,P受两个力作用平衡,Q受三个
Example 1 As shown in Fig. 1, the angle between two fixed and smooth hard rods OA and OB placed horizontally is θ, and the light rings P and Q on the two rods are connected by light ropes. The constant force is now used. F Pull the ring Q along the OB rod direction. When the two rings are stable, how much is the tension of the rope? The analysis converts the implied conditions in the question to dominant conditions: (1) Light ring → Gravity, smooth rod → Excluded Friction. (2) The ring is put on the rod → belongs to the point and line contact, P, Q are subjected to the direction of the elasticity perpendicular to the rod. (3) Two-ring stable → static state → F-closed = 0. In summary, P is Two forces balance, Q is affected by three