问题 问答题

襄阳汉江大桥是一座公、铁两用特大桥梁,其于1970年5月20日建成通车.大桥的铁路桥长892米.一列火车长100m,当车头距铁路桥桥头50m时开始由静止加速,其速度一时间图象如图所示,求:

(1)火车加速时的加速度大小;

(2)火车经过铁路桥的时间.

答案

(1)由速度-时间图象,可知在0-20s内

可得:a=

vt-v0
t
=1m/s2

(2)对火车在其加速阶段

20s内前进位移为:s=

1
2
at2=200m>50m

其前进50m所用时间为:t1=

2s
a
=10s

可知,加速阶段过桥时间为:t2=t-t1=20s-10s=10s

匀速阶段过桥时间为:t3=

s
v
=
100+892-(200-50)
20
=42.1s

故,火车过桥时间为:t=t2+t3=52.1s.

答:

(1)火车加速时的加速度大小是1m/s2

(2)火车经过铁路桥的时间是52.1s.

阅读理解

阅读理解。

     Listening is also important just like reading.   Although it's a bit more difficult, it helps you improve your

pronunciation and conversational skills.

     When you learn a foreign language, you should start to listen as soon as you can. This way you will get

familiar with the sounds of the language. Learning pronunciation will be much easier for you.

     It's a good idea to listen again and again to the same content (内容). Choose something interesting and

listen to it lots of times. While listening, try to remember useful sentences,   or even some passages.   Then

practice saying them for memory, imitating (模仿) the speaker's pronunciation. After a while, you will notice

that words and phrases   from  the recording become a part of you.   You will start using them in your own

sentences.

     Try to do some listening every day. The best way would be to have an MP3 player. Then you can listen

when you go to school or go for a walk.

     Remember to choose something you can understand and you like. Make sure the voice of the speaker is

pleasant. This way you will enjoy listening and look forward to doing it.

1. You should listen to English .

A. once a week

B. once a month

C. every day

D. every week

2. What should we listen to according to the passage?

A. Something we understand

B. Something interesting

C. Something difficult

D. Both A and B

3. Listening is reading.

A. more important than

B. less important than

C. as important as

D. easier than

单项选择题