学生在解动量题时有两种典型情况,第一,对物理模型类的题目,动量定理和动量守恒定律不能灵活应用。第二,应用动量守恒定律时,必要的物理过程分析不透。下面对此作一粗浅的分析。【例1】质量为m的小球在距地面高h处由静止自由落下,正落在沿光滑水平面以 v_0匀速行驶的装有砂子的小车中,如图1。车与砂子的总质量为M,当小球与小车相对静止时,小车的速度为 There are two typical situations in which students solve problems. First, the topics of physical models, the momentum theorem and the law of conservation of momentum cannot be applied flexibly. Second, when applying the law of conservation of momentum, the necessary physical processes are not thoroughly analyzed. Here is a rough analysis of this. [Example 1] A ball with a mass of m falls freely from a standstill at a height h from the ground and falls on a sand-laden car running at a constant speed along a smooth horizontal plane, as shown in Fig. 1. The total mass of the car and the sand is M. When the ball and the car are relatively stationary, the speed of the car is