平均速度似乎是力学中一个不太起眼的概念 ,同学们在解题中很少用到 .然而 ,对一些过程繁琐、运算复杂的习题 ,若利用平均速度来求解 ,可达到事半功倍的效果 .例 1　一物体做匀加速直线运动 ,在某时刻前的ｔ1 内的位移是ｓ1 ,在该时刻后的ｔ2 内的位移是ｓ2 ,则物体的加速度是 The average speed seems to be a less conspicuous concept in mechanics. Classmates rarely use it in problem solving. However, if some of the processes are cumbersome and computationally complex, the average speed can be used to solve the problem. 1 When an object performs uniform acceleration and linear motion, the displacement in t1 before a certain moment is s1, and the displacement in t2 after that moment is s2, then the acceleration of the object is