问题 选择题

两个弹性小球相向运动发生碰撞的短暂过程中,两个球同时依次经过减速、停止又反向运动的几个阶段,关于这两个球碰撞前的情况有以下叙述,以下判断正确的是

①两个球的质量一定相等 ②两个球的动量大小一定相等 ③两个球的速度大小与其质量成反比 ④两个小球碰撞过程中交换速度

A.①②③④

B.①②③

C.②③④

D.②③

答案

答案:D

两弹性小球相向碰撞过程中,总动量守恒,由两球同时停止知道两球总动量为零,即两球的碰前动量一定等大反向;由于其质量不一定相同,若碰撞后速度交换,则其碰后总动量方向与碰前总动量方向可能相反(若两球质量不等时),即①④错,②③正确,应选D.

阅读理解

阅读理解。

     Chinese Valentine's Day (情人节) is on the seventh day of the seventh month of the lunar calendar (阴历).

It is a traditional festival for Chinese people. It comes from a romantic ancient Chinese story. Niu Lang and

Zhi Nv, two lovers who got separated by the Queen Mother of the Western Heavens, can only meet that night.

Thanks to this touching story, Chinese people regard the seventh day of the seventh month of the lunar calendar as Chinese Valentine's Day. In China people also call it "Qixi".

     Meanwhile, February 14 of the solar calendar is European Valentine's Day. It is related to a moving story

too. The story goes that, there was a cruel king in ancient Rome whose name was Claudius. He forbade the

youth to get married during the wars, which made the lovers angry. There was a monk (修道士) named

Valentine who was very angry at the rule and the king. One day a couple of lovers came to his temple to ask

for help to get married. Valentine helped them. Later, many couples got married with Valentine's help. But

Claudius knew it soon. He put Valentine to death cruelly. And that day was February 14, the year of 270.

     Compared with European Valentine's Day, Qixi is less popular in China though it is a traditional Chinese

festival. There may be many reasons. First of all, the lunar calendar is not easy to remember for most of the

young people who are used to the solar calendar. Secondly, to many businessmen, European Valentine's Day is

not only a festival for lovers but also a good chance to make money. Most of the flower shops can sell their

flowers at a good price on European Valentine's Day while the business drops in Qixi, because on European

Valentine's Day lovers know more about how to enjoy it. They exchange cards, flowers and go out to date.

But most of them don't know the culture of Chinese Valentine's Day or how to celebrate it.

1. This text is mainly about ______.

A. two moving romantic stories

B. something about Qixi and Valentine's Day

C. why young people prefer Western festivals

D. how Qixi is different from European Valentine's Day

2. Qixi is less popular than European Valentine's Day because _____.

A. businessmen think that European Valentine's Day is more important than Qixi

B. the government encourages people to celebrate foreign festivals

C. the costs on Qixi are higher than those on European Valentine's Day

D. the lunar calendar is not easy to remember and people don't know how to enjoy Qixi

3. Which of the following statements is TRUE according to the text?

A. Lovers exchange cards, flowers and go out to date on Qixi.

B. Valentine helped a couple of lovers kill the cruel king.

C. European Valentine's Day was named after a person.

D. Old people in China dislike young people celebrating European Valentine's Day.

4. If the text goes on, what will probably be talked about in the next paragraph?

A. Young people should fight for love and happiness.

B. Chinese people should treasure traditional Chinese festivals more.

C. Qixi will also become an international festival in the future.

D. Chinese people should stop celebrating European Valentine's Day.

单项选择题