有一类物理竞赛题,数字的已知量很少,文字叙述较长,未知量较多,看起来觉得无从下手,怎样解这类题目,下面以两例说明. 例1 一通讯员从一列长为a,正在匀速前进的队伍的排尾以不变的速度赶到排头,又立即以等大的速度返回排尾,这时队伍前进的 There is a class of physics contest questions, the number of known numbers is small, text description is longer, the amount of unknowns is more, it seems that there is no way to start, how to solve such problems, the following two examples. Example 1 A correspondent from a column for a. The ranks of the team that is moving forward at a constant speed reach the top of the line at a constant speed, and immediately return to the end of the line at the same speed. At this time, the team advances.