原题.如图1所示,两条平行导轨所在平面与水平地面的夹角为θ,间距为L.导轨上端接有一平行板电容器,电容为C.导轨处于匀强磁场中,磁感应强度大小为B,方向垂直于导轨平面.在导轨上放置一质量为m的金属棒,棒可沿导轨下滑,且在下滑过程中保持与导轨垂直并良好接触.已知金属棒与导轨之间的动摩擦因数为μ,重力加速度大小为g.忽略所有电阻.让金属棒从导轨上端由静止开始下滑,求: As shown in Figure 1, the angle between the plane where the two parallel rails are located and the horizontal ground is θ and the distance is L. The upper end of the guide rail is connected with a parallel-plate capacitor with a capacitance of C. The guide rail is in a uniform magnetic field, Is B, the direction perpendicular to the plane of the guide rail. Place a mass of metal rods on the rail m, the rod can slide along the rail, and in the process of sliding down perpendicular to the rail and good contact known dynamic friction between the metal rod and the rail The factor is μ and the magnitude of the gravitational acceleration is G. Ignoring all the resistance, let the metal rod slide down from the upper end of the guide rail at rest, and find: