题目:如图1所示,在长为L的轻杆中点A和端点B各固定一个质量均为m的小球,杆可绕无摩擦的轴O转动,使杆从水平位置无初速释放摆下.求当杆转到竖直位置时,A球和B球的速度分别多大?错解:在A、B两球的质心处等效认为有一个小球C,如图1所示,则mC=2m,LOC=3L4,设杆绕O点转动的角速度为ω Title: As shown in Fig. 1, in the mid-points A and B of the light rod of length L, a small ball of mass m is fixed, and the rod can be rotated around the non-frictional axis O so that the rod is released from the horizontal position without initial velocity. Swing down. Seeking when the rod is turned to the vertical position, how fast are the speeds of the A ball and the B ball? The wrong solution: At the center of mass of the two balls A and B, there is an equivalent ball C, as shown in Figure 1. Then mC = 2m, LOC = 3L4, set the rod to rotate around the O point angular velocity is ω