问题 问答题

一列火车进站前先关闭气阀,让车减速滑行.滑行了300m时速度减为关闭气阀时的一半,此后又继续滑行了20s停在车站.设火车在滑行过程中加速度始终维持不变,试求:

(1)火车关闭气阀时的速度和加速度;

(2)从火车关闭气阀到停止滑行时,滑行的总位移.

答案

(1)设火车的初速度为v0,由速度位移公式得

(

v0
2
)2-v02=2as1

由速度时间公式得

:0=

v0
2
+at2

代入数据解得:

v0=20 m/s,a=-0.5 m/s2

(2)由2as2=(

v0
2
)2得最后20s内的位移为:

s2=100 m

则有:s=s1+s2=300+100=400 m.

答:(1)火车滑行的加速度a=-0.5 m/s2,火车关闭气阀时的速度为20m/s

(2)从火车关闭气阀到停止滑行时,滑行的总位移400m.

完形填空

阅读理解

     I had a summer camp with my classmates last year.

     Early in the morning, we gathered at the bus station. After saying goodbye to our parents, .we got on the buses. It

took us more than two hours to arrive at the camp ground.

     We got off the buses cheerfully. Laughing and shouting, we jumped and ran all over the place. It was the first time

for us to be away from the parents. Some of us started to feel homesick. However, when the night party and dances

began, the homesickness was gone.

     The next day, everybody rushed to the boating class, hoping to be at the head of the others. At first, my friends and

I worked hard, but the boat wouldn't listen to us and kept going round and round. Then the teacher taught us how to

work together. After many tries, we did much better.

     Swimming class was my favourite. It was about the hottest time of a day and the best time to stay in the cool water.

The swimming teacher was a funny man, and during the class he often made us laugh happily.

     During the week I learned a lot of new things and made many new friends. I also learned how to take care of myself.

1. They got to the camp ground _____.

A. on foot

B. by bike

C. by bus

D. by plane

2. The camp ground was _____ from their homes.

A. quite near

B. not far

C. very long

D. quite far

3. Why swimming class was the writer's favorite?

A. Because it was good to stay in the cool water when the weather was hot.

B. Because the writer felt quite relaxed during the class.

C. Because the swimming teacher was interesting.

D. Because of all the above.

4. Which statement is NOT true?

A. The children were happy to be away from Dad and Mum.

B. Their homesickness lasted for long.

C. It was teamwork to boat.

D. They camped for a week.

5. Which is the best title for the passage?

A. I Learnt a Lot.

B. Boating and Swimming.

C. On the Camp ground.

D. My First Summer Camp.

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