题目

Do you know that a fast reader can get the ideas better than a slow reader can? Of course, you save time by reading fast, but it is not the main reason for fast reading. The main reason is that you understand better what you are reading when you read fast. As your eyes move along the line of a book, they make fixations (注视).It is important that you see several words at a fixation. It is also important that your eyes leave a group of words quickly and move on to another group. The number of letters or words that you see at a fixation are called your eye span(视福).With practice you can le14．以18m/s的速度行驶的汽车，紧急刹车后做匀减速直线运动，其加速度大小为6m/s2，求：（1）汽车2s末的速度；（2）汽车什么时候停下来；（3）汽车在6s内通过的位移．