生成讲解视频---**12.** **Question Stem:** 将物体放置在静止不动的水平传送带上。用水平拉力 F 向右拉动物体，使其做向右的匀速直线运动时，受到的滑动摩擦力为 F₁₁。当传送带在转轴的带动下向左运动时，再用水平向右的力拉动该物体，使其仍做向右的运动，如图 8.3-4 所示，此时物体受到的滑动摩擦力为 F₁₂。关于 F₁₁ 和 F₁₂ 的大小关系，下列说法正确的是 (C)。 **Translation of Question Stem:** An object is placed on a stationary horizontal conveyor belt. When a horizontal pulling force F pulls the object to the right, causing it to move in a uniform linear motion to the right, the sliding friction force it experiences is F₁₁. When the conveyor belt moves to the left driven by its rollers, and the object is again pulled by a horizontal force to the right, causing it to still move to the right, as shown in Figure 8.3-4, the sliding friction force experienced by the object at this time is F₁₂. Regarding the relationship between the magnitudes of F₁₁ and F₁₂, which of the following statements is correct (C). **Options:** A. F₁₁ > F₁₂ B. F₁₁ < F₁₂ C. F₁₁ = F₁₂ D. 无法判断 (Cannot determine) **Chart/Diagram Description:** * **Type:** Schematic diagram depicting an object on a conveyor belt. * **Main Elements:** * A conveyor belt system is shown, consisting of a horizontal belt supported by two circular rollers (one on the left, one on the right). * A rectangular object rests on the top surface of the horizontal conveyor belt. * A horizontal arrow labeled "F" extends from the right side of the rectangular object, pointing to the right, indicating a force applied to the object. * Inside the circular rollers, curved arrows indicate their rotation: * The left roller has a counter-clockwise arrow. * The right roller has a clockwise arrow. * These rotations imply that the top surface of the conveyor belt is moving to the left. * **Label:** The diagram is labeled "图 8.3-4" (Figure 8.3-4) below the conveyor belt system.