题如图1所示,足够长的金属导轨 MN 和 PQ与电阻 R 相连,平行地放在水平桌面上,质量为 m的金属杆 ab 可以无摩擦地沿导轨运动,导轨与 ab 杆的电阻不计,导轨的宽度为 L,磁感应强度为 B 的匀强磁场垂直穿过整个导轨平面,现给金属杆 ab 一个瞬时冲量I_0,使 ab 杆向右滑行,求最终杆在磁场中滑行的位移多大? As shown in Figure 1, long enough metal rails MN and PQ are connected to resistor R, placed parallel on a horizontal table, metal rod ab of mass m can move along the rails without friction, and the resistances of rails and ab rods are not counted. The width of the guide rail is L, and the uniform magnetic field with the magnetic induction intensity B passes through the entire rail plane vertically. Now give a momentary impulse I_0 to the metal rod ab, so that the ab rod slides to the right, and how large is the final rod’s displacement in the magnetic field?