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高考题是否科学严谨历来备受瞩目,2013年新课标Ⅰ卷第25题就受到很多质疑.原题.如图1,两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.导轨处于磁场强度为B的匀强磁场中,方向垂直导轨平面.在导轨上放置一质量为m的金属杆,金属杆可沿导轨下滑,金属杆与导轨间的动摩擦因数为μ,重力加速度为g,忽略所有电阻.让金属棒由静止开始下滑,求:
The scientific entrance exam questions have always been highly scrutinized, 2013 New Curriculum I Volume 25 questions are subject to many questions. As shown in Figure 1, the two parallel rails where the angle between the plane and the horizontal ground θ, the spacing 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 with a magnetic field strength of B and is oriented perpendicular to the plane of the guide rail.A metal rod of mass m is placed on the guide rail and the metal rod slides along the guide rail, The dynamic friction coefficient between the rod and the guide rail is μ, the acceleration of gravity is g, ignoring all the resistance. Let the metal rod start to glide from rest, find: