问题 问答题

小明在假期赴外地探望外祖母,他乘坐车时发现,每经过铁轨接头处,车身都要振动一次,他还发现,火车进山洞前一瞬间要鸣笛一次.小明恰好坐在车尾,从听到鸣笛声到车尾出洞,小明共数出85次车身振动,所用的时间是1min45s.若车身总长175m,每节铁轨长12.5m,求当时火车的速度是多少?山洞的长度是多少?(假设火车一直匀速直线行驶,声音在空气中的传速度是340m/s)

答案

已知:车长s1=175m,听到鸣笛后的行驶时间t=1min45s=105s,车在105s内行驶的距离s=(85-1)×12.5m=1050m,

求:火车的速度v=?;山洞长度L=?

(1)火车的速度v=

s
t
=
1050m
105s
=10m/s;

(2)∵v=

s
t

∴听到鸣笛声的时间t1=

s1
v+v
=
175m
10m/s+340m/s
=0.5s,

在听到鸣笛声之前车行驶的距离:s2=vt1=10m/s×0.5s=5m,

山洞长度L=s+s2-s1=1050m+5m-175m=880m.

答:火车行驶的速度为10m/s;山洞的长度为880m.

阅读理解

阅读理解。

     Joe and Helen Mills had two little children. One was six and the other four. They

always resisted going to bed, and Helen was always complaining (抱怨) about this and asking Joe for help.  But as he did not come home until after they had gone to bed

during the week, he was unable to help except at weekends.

    Joe considered himself a good singer, but really his voice was not at all musical.

However, he decided that, if he sang to the children when they went to bed, it would

help them to relax, and they would soon go to sleep,

     He did this every Saturday and Sunday night until he heard his small son

whispered to his younger sister, "If you pretend that you're asleep, he stops. "  

1. The children always resisted going to bed, which          .

A. made Joe suffer a lot

B. satisfied their mother

C. Helen was not satisfied with

D. gave Helen much happiness

2.  The husband couldn't help the wife to look after the children          .      

A. because he returned from work too late every day

B. since his voice sounded like a singer's

C. except on Saturday and Sunday

D. for he did not come home until after the children had gone to bed at weekends

3. Joe worked         .

A. all the week including Saturday and Sunday

B. during the week including the weekends

C. every day but Saturday and Sunday

D. every week except on Sunday     

4. Which of the following conclusions can we draw from the above story?

A. Joe's song did help the children to relax.

B. With Joe's help, the children went to sleep.

C. The wife must be thankful to her husband for the great help.

D. The children were so tired of their father's voice that they pretended to be asleep.

5. This joke tells about          .

A. Joe and Helen

B. Helen's trouble

C. Joe's foolery

D. the bright idea of the two small children

综合