问题 选择题

质点在某段时间内做曲线运动,则在这段时间内(  )

A.速度一定不断改变,加速也一定在不断改变

B.速度一定在不断改变,加速度可能不变

C.速度可能不变,加速度一定在不断改变

D.速度可能不变,加速度也可能不变

答案

答案:B

解:物体既然是在做曲线运动,它的速度的方向必定是改变的,但是合力不一定改变,所以加速度不一定改变,如平抛运动,所以A错误,B正确.

既然是曲线运动,它的速度的方向必定是改变的,那么速度也就一定在变化,所以CD错误.

故选B.

阅读理解

阅读理解。

     Before you go to another country it is a great help if you know the language and some of the customs

(风俗) of the country.

     When people meet each other for the first time in Britain, they say "How do you do?" and shake hands

(握手). Usually they do not shake hands when they just meet or say goodbye. But they shake hands when

they haven't met for a long time or when they will be away form each other for a long time.

     Last year a group of German students went to England for a holiday. Their teacher told them that the

English people hardly ever shake hands. So when they met their English friends at the station, they kept

their hands behind their backs. The English students had learned that the Germans shake hands as often

as possible, so they put their hands in front and got ready to shake hands with them. It made both of them

laugh.

1. It is _____ if you know the language and some of the customs of a country before you pay a visit to that

    country. [ ]

A. not useful

B. not helpful

C. very helpful

D. very bad

2. English people usually shake hands when they _____. [ ]

A. meet every time

B. meet for the first time

C. say goodbye to each other

D. say hello to each other

3. Usually, English people don't shake hands _____. [ ]

A. when they will be away for a long time

B. when they say "How do you do?"

C. when they just meet or say goodbye

D. when they haven't met for a long time

4. Which is right?[ ]

A. German people shake hands as often as possible.

B. English people like shaking hands very much.

C. German people hardly ever shake hands.

D. Both English people and Germans don't like shaking hands.

5. This story is about _____. [ ]

A. shaking hands

B. languages

C. customs

D. languages and customs

多项选择题