题:如图1所示,质量都是m的两个小球,分别固定在一长为l的轻杆的中点和一端.整个装置从水平位置绕固定端O下落到竖直位置时,两球的速度分别是多大?图1笔者在教学中发现部分学生用等效法求解,即用A、B两球的重心C代替A、B两球,先求出重心C到达竖直位置C′时的速度vC′,再分别求出 Question: As shown in Figure 1, two balls of mass m are fixed at the midpoint and one end of a long light bar. When the entire device is dropped from the horizontal position around the fixed end O to the vertical position, What is the speed of the two balls? Figure 1 The author found that some students use the equivalent method to solve the problem, that is, using the center of gravity C of A and B to replace the two balls A and B. First, find the center of gravity C to reach the vertical position C′. Speed ​​vC′, then find