1.已知题目答案：1）aA=3.5m/s2；aB=10m/s2；2）t=2.5s；3）9.75m；2.生成的视频需要有声音；3.讲解过程包含以下内容：1、知识目标 掌握滑块 - 木板模型中摩擦力方向的判断方法 熟练运用牛顿第二定律分析多物体加速度 学会通过临界状态（共速点）划分运动阶段并分段求解 理解相对位移与划痕长度的物理意义及计算方法 2、能力目标 培养隔离法受力分析能力与运动过程建模能力 提升临界条件判断与多阶段问题的逻辑拆解能力 3、素养目标 体会物理模型在解决实际问题中的应用价值 养成严谨的科学思维习惯（如分阶段验证、易错点排查）---**Text Extraction:** 如图所示，质量 M=2 kg 的木板 A 放在水平地面上，当 A 向右滑动的速度 v₀=13.5 m/s 时，在 A 中间位置轻轻地放上一个大小不计、质量 m=1 kg 的小煤块 B, 同时给 B 施加一个水平向右的 F=6 N 的恒力作用并开始计时。已知 A 与地面间的动摩擦因数 μ₁=0.1, A 与 B 间的动摩擦因数 μ₂=0.4。(设滑板 A 足够长, g 取 10 m/s²) 求： (1) 开始时 A、B 的加速度分别为多大; (2) 经多长时间, 小煤块 B 的速度达到 13 m/s; (3) 3s 时小煤块 B 在木板 A 上留下了多长的划痕。 **Parameters and Constants:** Mass of A: M = 2 kg Initial velocity of A: v₀ = 13.5 m/s (to the right) Mass of B: m = 1 kg Force on B: F = 6 N (horizontal, to the right) Coefficient of kinetic friction between A and the ground: μ₁ = 0.1 Coefficient of kinetic friction between A and B: μ₂ = 0.4 Acceleration due to gravity: g = 10 m/s² Condition: Plank A is long enough. **Questions:** (1) What are the accelerations of A and B initially? (2) How long does it take for the velocity of block B to reach 13 m/s? (3) At 3s, how long is the scratch left by block B on plank A? **Chart/Diagram Description:** * **Type:** Schematic diagram showing two blocks stacked on a surface with forces and initial velocity indicated. * **Main Elements:** * Horizontal Ground: Indicated by hatching lines. * Block A: A rectangular block labeled "A" resting on the ground. * Block B: A smaller rectangular block labeled "B" resting on top of block A. * Force F: An arrow labeled "F" originating from block B and pointing horizontally to the right, indicating a force applied to B. * Initial Velocity v₀: An arrow labeled "v₀" originating from the right side of block A and pointing horizontally to the right, indicating the initial velocity of A.