问题 计算题

(10分)汽车正以的速度在平直公路上行驶,突然发现正前方有一辆自行车以的速度作同方向的匀速直线运动,汽车立即关闭油门作加速度大小为的匀减速运动,汽车恰好没有碰上自行车,求关闭油门时汽车与自行车的距离。

某同学是这样解的:

汽车关闭油门后的滑行时间和滑行距离分别为:

在相同时间内,自行车的前进的距离为:

关闭油门时汽车与自行车的距离为:

你认为这位同学的解法是否合理?若合理,请完成计算;若不合理,请用你自己的方法算出正确结果.

答案

“不合理”

题目分析:“不合理”

理由:能满足题设的汽车恰好不碰上自行车的临界条件是:当汽车减速到与自行车速度相等时,它们恰好相遇,而不是汽车减速到0时相遇。

正确解法:

汽车减速到与自行车速度相等时,所用时间为:t=(v1-v2)/a=10s

在此时间内,汽车滑行距离为:s1=(v21-v22)/2a=70m

自行车的前进的距离为:s2=v2t=40m

关闭油门时汽车与自行车的距离为:s=s1-s2=30m

单项选择题
改错题

第二卷(共35分)

第四部分:写作(共两节,满分35分)

第一节:短文改错(共10小题;每小题1分,满分10分)

此题要求改正所给短文中的错误。对标有题号的每一行作出判断:如无错误,该行右边横线上画一个勾(√ );如有错误(每行只有一个错误,则按下列情况改正:

此行多一词:把多余的词用斜线(/)划掉;在该行右边的横线上写上该词,并也用斜线划掉。

此行缺一词:在缺词处加一个漏字符(∧),在该行右边的横线上写上该加的词。

此行错一词:在错的词下划一横线,在该行右边横线上写出改正后的词。

注意:原行没有错的不要改。

Mary was an university student . She didn’t have very much  76.      

money and her parents were not rich , and she had an uncle           77.      

who had been fortunate enough to collect great wealthy . He     78.      

always gave her valuable Christmas and birthday present .      79.      

When her uncle’s birthday came round , Mary want to buy him 80.      

something real special , but because he was rich , she did not    81.      

know how to get him . She went into the best shop in her      82.      

town and explained what her problem was to one of helpful          83.      

shop assistants . Finally she asked , “What do you have for       84.      

someone who has already got everything he wants or needs to ?”  85.      

The assistant sighed deeply and answered , “Envy , only envy.”