这个题怎么做？---**Question Number:** 15 **Question Stem:** 如图所示，两平行光滑长直金属导轨水平放置，间距为L。abcd区域有匀强磁场，磁感应强度大小为B，方向竖直向上。初始时刻，磁场外的细金属杆M以初速度v₀向右运动，磁场内的细金属杆N处于静止状态。两金属杆与导轨接触良好且运动过程中始终与导轨垂直。两杆的质量均为m，在导轨间的电阻均为R，感应电流产生的磁场及导轨的电阻忽略不计。 **(1)** 求M刚进入磁场时受到的安培力F的大小和方向； **(2)** 若两杆在磁场内未相撞且N出磁场时的速度为v₀/3，求：①N在磁场内运动过程中通过回路的电荷量q；②初始时刻N到ab的最小距离x； **(3)** 初始时刻，若N到cd的距离与第（2）问初始时刻N到ab的距离相同、到ab的距离为kx(k>1)，求M出磁场后不与N相撞条件下k的取值范围。 **Image Description:** * **Type:** Schematic diagram illustrating a physics problem involving magnetic fields and moving conductors on rails. * **Main Elements:** * Two parallel horizontal lines representing smooth long straight metal rails. * A region labeled `abcd` representing a uniform magnetic field. This region is bounded by four lines: `ab` (slanted), `bc` (along the lower rail), `cd` (slanted), and `da` (along the upper rail). The lines `ab` and `cd` are depicted as slanted dashed lines. * Two vertical upward arrows labeled `B` are shown within the `abcd` region, indicating the direction of the magnetic field (vertically upward). * A vertical double-headed arrow labeled `L` is shown between the rails to the right of the `abcd` region, indicating the distance between the rails. * A straight line segment labeled `M` is shown on the rails to the left of the `abcd` region, representing a metal rod. An arrow labeled `v₀` points to the right from rod M, indicating its initial velocity. * A straight line segment labeled `N` is shown on the rails within the `abcd` region, representing another metal rod. * The points defining the magnetic field region are labeled `a` (upper left corner of the region), `b` (lower left corner), `c` (lower right corner), and `d` (upper right corner). `a` and `d` are on the upper rail, `b` and `c` are on the lower rail. The lines connecting a-b and c-d are slanted. **Other Relevant Text:** None beyond the question stem and sub-questions.