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例1 如图1所示,同一竖直平面内固定着两根水平绝缘细杆AB、CD,长均为L,两杆的竖直距离为h,两杆在B、D两端与光滑绝缘的半圆形细杆相切,O为AD、BC连线的交点.在O点固定一电量为Q的正电荷,质量为m的小球P带正电,电量为q,穿在细杆上,从A以一定的初速度出发,沿杆滑动,最后可到达C点.已知小球与两水平杆之间的动摩擦因数为μ,小球所受的库仑力始终小于重力.求: (1)P在水平细杆上滑动时所受摩擦力的极大
Example 1 As shown in Figure 1, two horizontal insulating rods AB and CD are fixed in the same vertical plane, the length is L, and the vertical distance between two rods is h. The two rods are insulated from the smooth ends of B and D. The semi-circular rod is tangent, O is the intersection point of the AD and BC wires. At point O, a positive charge of Q is fixed, and the mass of ball P is positive, the charge is q, and it is worn on the rod. From A, starting from a certain initial speed, sliding along the rod, and finally reach point C. The dynamic friction coefficient between the known ball and the two horizontal rods is μ, and the Coulomb force on the pellet is always smaller than the gravity. (1)P is greatly affected by friction when sliding on a horizontal rod