问题 填空题

2005年10月12日,我国成功发射“神舟六号”载人飞船,两名宇航员空间试验顺利完成,并于10月17日凌晨顺利返回.

(1)据报道:飞船1天绕地球飞行约16圈,已知地球的半径R=6400Km,地球表面的重力加速度g=9.8m/s2,飞船在圆轨道上运行.试估算飞船距地面的高度约为______Km;

(2)飞船进入正常轨道后,因特殊情况而需要降低到新轨道上绕地球运行,那么在新轨道上飞船的线速度与原轨道时相比将______(选填“变大”、“变小”或“不变”).

答案

(1)飞船做匀速圆周运动,万有引力提供向心力,得

   G

Mm
(R+h)2
=m
4π2
T2
(R+h)

在地球表面上,有G

Mm′
R2
=mg

联立上两式得 h=

3
gR2T2
4π2
-R

而周期T=

24×3600
16
s=5400s,

代入数据解得,h=270km

(2)根据卫星的线速度公式v=

GM
r
知,飞船轨道半径越小,线速度越大,故在新轨道上飞船的线速度与原轨道时相比变大.

故答案为:

(1)270;

(2)变大

单项选择题
阅读理解

I was standing in the kitchen helping with dinner, asking my mom about my brother's doctor ' s  appointment. They  were  testing  him for  autism(自闭症 ) .  My  brother, Captain, four  years old at the time, had always been my best friend. We would wrestle, play games and have the best of times together, even though we were far apart in age. My mom told me about the appointment, but ,when she got to the point about the test, she  stopped. I turned around  and  she had tears  in her eyes. I  stared  at her, wishing she would say  something , when  I realized what that  silence meant. My eyes  got blurry (模糊的 )  and  my  breathing  got  very  ragged.  " The  test was positive , sweetheart , "  she said. I broke down, crying.

My mom was trying to cool me down, saying that Captain couldn't see me like this and I had to be a big girl , when the front door opened, and Captain, our three-year-old sister Cali, and  my father came in. I walked out of the kitchen. I couldn't look at him. Everything had just  changed. He was no longer that little baby brother who was just a normal little boy.

We had to move a while later because Captain needed treatment. One day ,I was standing  in the bus line waiting when the " short bus"  came and picked some kids up. The children in  the other line started making jokes about the " retards(智力迟钝者) "  on that bus and I felt a  strange feeling in my stomach, ,which I had never felt before.

During a band class, my teacher, Mrs. Young, stopped our playing to give us some feed-  back. " Guys ,we ' re playing like the kids on the short bus !  Come on!"  I felt that same feeling I had in the bus line. The entire room was laughing when I raised my hand.  " Yes , Alexis?"  Mrs. Young asked. "I don't think we should make fun of the short bus, because there are a lot of people on  that bus who have great personalities and have the same feelings as we do. And also ,I know  some people on those buses and they are some of the most caring, sweetest, and smartest people , so I would appreciate it if you didn't make fun of them. "

Everyone stared at me. Mrs. Young apologized for the comment and then started the song again.

小题1: What did Alexis think her mother' s silence mean in Paragraph One?

A.There was no chance for Alexis to play games with Captain.

B.Captain was likely to miss the appointment.

C.Captain really suffered from autism.

D.Alexis had to prepare dinner quickly.小题2: Why did Alexis go out of the kitchen?

A.Because she didn't want to help with dinner.

B.Because she would be much sadder looking at Captain.

C.Because she wanted to play with Captain outside.

D.Because she wasn't willing to meet a sick brother.小题3:What Alexis said to her teacher can be seen as a kind of         .

A.threat

B.approval

C.apology

D.condemnation小题4: Which of the following would be the best title for the passage?

A.Speaking up.

B.Giving up.

C.Looking .up.

D.Taking up.