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八年级(理论部分) 1、半径为R的滑轮紧固在半径为r的圆柱体上,组成一个双层滑轮,安在轴O上(图1)。绳子的一端穿过滑轮系在墙壁上,绳子的另一端绕在圆柱上,垂下的绳子还绕过一只直径为D的滑轮,这个滑轮下面悬挂着质量为M的重物;由于D=R+r,因而下垂的那部分绳子在竖直方向。整个滑轮系统处于平衡,轴O的摩擦力忽略不计。试求绳中A处的张力多大? 答:F_张=Mg/2(1-r/R)。
Grade 8 (theoretical) 1. The pulley with the radius R is fastened to a cylinder with a radius of r and forms a double-layer pulley mounted on the shaft O (Figure 1). One end of the rope was passed through the pulley and was tied to the wall. The other end of the rope was wound around the cylinder. The hanging rope also passed around a pulley of diameter D. Below this pulley, a weight of mass M was hung; since D=R +r, so the part of the rope that hangs is in the vertical direction. The entire pulley system is in balance and the shaft O friction is negligible. Try to find the tension in the rope at A? A: F_Zhang = Mg/2(1-r/R).