请你做出我上传题目的讲解视频---**Question 16** **(2024 德阳, 9)** **Question Stem:** 如图所示，分别用甲、乙两种形式的滑轮组把重为 400N 的物体匀速向上提起；已知每个滑轮重 20N，忽略绳子的重力以及滑轮与绳子的摩擦，图甲中车对绳子的拉力为______N，图乙中人对绳子的拉力为______N。 **Translation of Question Stem:** As shown in the figure, pulley systems in two forms, Jia and Yi, are used to lift an object weighing 400N upwards at a constant speed; it is known that each pulley weighs 20N, neglecting the weight of the rope and the friction between the pulley and the rope. The pulling force exerted by the vehicle on the rope in Figure Jia is ______ N, and the pulling force exerted by the person on the rope in Figure Yi is ______ N. **Given Information:** * Weight of the object: G_object = 400 N * Weight of each pulley: G_pulley = 20 N * Motion: lifted upwards at a constant speed. * Assumptions: Neglect the weight of the rope and friction between the pulley and the rope. **Diagram Description:** **Overall:** Two diagrams, labeled 甲 (Jia) and 乙 (Yi), show different pulley systems used to lift a heavy object. Both systems are attached to a horizontal bar at the top. **Diagram 甲 (Jia):** * Type: Pulley system diagram. * Components: * Horizontal bar at the top. * One fixed pulley attached to the bar on the left. * One movable pulley attached to the object below. * A rope passes around the fixed pulley, then around the movable pulley, and one end is pulled horizontally by a tractor. * An object (rectangular box) is attached to the movable pulley. * An upward arrow indicates the direction of motion of the object. * A tractor (vehicle) is shown on the right, pulling the horizontal end of the rope. * Label: "图甲" (Figure Jia) below the diagram. * Pulley configuration: One fixed and one movable pulley. The movable pulley supports the object. The rope segment pulling upwards on the movable pulley is vertical. The horizontal rope segment is pulled by the tractor. **Diagram 乙 (Yi):** * Type: Pulley system diagram. * Components: * Horizontal bar at the top. * One fixed pulley attached to the bar on the right. * One movable pulley attached to the object below. * A rope is attached to the horizontal bar on the left, passes around the movable pulley, then around the fixed pulley, and the other end is pulled downwards and to the right by a person. * An object (rectangular box) is attached to the movable pulley. * An upward arrow indicates the direction of motion of the object. * A person is shown on the right, pulling the rope downwards and to the right. The person appears to be exerting significant effort (indicated by sweat drops). * Label: "图乙" (Figure Yi) below the diagram. * Pulley configuration: One fixed and one movable pulley. The movable pulley supports the object. The rope is anchored to the fixed support. Two rope segments pull upwards on the movable pulley (one from the anchor point, one from the fixed pulley). The person pulls the free end of the rope. **Fill-in-the-blanks:** * 图甲中车对绳子的拉力为______N * 图乙中人对绳子的拉力为______N **Calculation Notes (Not part of extracted content, but for understanding):** * In both cases, the object is lifted at constant velocity, so the net force is zero. * In Figure 甲, the movable pulley is supported by 2 segments of the rope. One segment is vertical, and the other goes to the fixed pulley. The force F is applied to the free end of the rope. Let's re-examine the diagram for Figure 甲. The rope goes from the tractor, around the movable pulley, then up to the fixed pulley. The object is attached to the movable pulley. The rope segment going upwards from the movable pulley is attached to the fixed support. So, the object and the movable pulley are supported by *two* segments of the rope pulling upwards from the movable pulley. The force F is applied by the tractor pulling the free end. The segments supporting the movable pulley are pulling upwards. One segment is vertical (to the fixed support). The other segment goes around the fixed pulley and is pulled by the tractor. So, in Figure 甲, there are 2 vertical segments of rope supporting the movable pulley and the object. The pulling force F is applied to the free end of the rope after it passes through the fixed pulley. Therefore, the total upward force on the movable pulley and the object is 2F. * In Figure 乙, the rope is attached to the fixed support on the left, goes down around the movable pulley, then up to the fixed pulley on the right, and the person pulls the free end. The movable pulley and object are supported by *two* segments of the rope pulling upwards. One segment is vertical (from the anchor point). The other segment goes around the fixed pulley and is pulled by the person. So, the total upward force on the movable pulley and the object is 2F, where F is the force applied by the person. * In both cases, the total upward force by the rope segments equals the total downward force (weight of object + weight of movable pulley), assuming constant velocity and neglecting friction and rope weight. * So, 2F = G_object + G_pulley. * 2F = 400 N + 20 N = 420 N. * F = 420 N / 2 = 210 N. * This calculation applies to both Figure 甲 and Figure 乙 because the pulley system configuration is the same (one fixed, one movable, and the movable pulley is supported by 2 rope segments) and the conditions are the same. Therefore, the pulling force in Figure 甲 is 210 N, and the pulling force in Figure 乙 is 210 N.