问题 选择题

2011年美国国家航空航天局(NASA)发现了可能存在生命的行星“开普勒22b“,它与地球相隔600光年,半径约为地球半径的2.4倍.“开普勒22b”绕恒星“开普勒22”运动的周期为290天,轨道半径为R1,地球绕太阳运动的轨道半径为R2,测得R1:R2=0.85.由上述信息可知,恒星“开普勒22”与太阳的质量之比约(  )

A.0.1

B.1

C.10

D.100

答案

行星绕恒星运动,万有引力提供向心力,有:G

Mm
r2
=m
4π2
T2
r

所以有:M=

4π2r3
GT2

所以恒星“开普勒22”的质量为:M1=

4π2R13
GT12

同理太阳的质量为:M2=

4π2R23
GT22

所以有:

M1
M2
=(
R1
R2
)3(
T2
T1
)
2
=(0.85)3×(
365
290
)
2
≈1,故B正确,ACD错误.

故选:B.

阅读理解

阅读理解。

     Students learn their lessons in class. In class teachers teach them. Students sit in the classroom listening.

 This is a way of learning. Is this the only way for students to learn something? Of course not. There is

 another way to learn. That is, students can teach themselves. For example, if you can not remember

 something when you are doing your homework, you can look at your book to find the answer. This is a

 way to teach yourself. And it is not a difficult thing. We can do this at any place and at any time.

     How do you teach yourself? The first thing you must do is reading. Read something you are interested

  in, or you have to read. The second is that you must ask yourself questions. If the question is something

 you don't understand or you want to know more about, you can write down these questions. The third is

 to answer the question yourself by thinking hard, by reading the text or other books, and sometimes by

 asking other people. This is the way of teaching yourself. And you must do this all by yourself. If you keep

  doing like this for a long time. You are sure to succeed (成功) in your study.

l. Listening to the teacher is _____ for students to learn something.

    A. not a way          

    B. the best way      

    C. the only way      

    D. not the only way

2. Which of the following is right?

    A. A student can teach himself only in class.

    B. It is a bad way to learn from the teacher.

    C. A student can learn to teach himself if he wants to.

    D. Students know very well how to teach themselves.

3. In teaching yourself, the first thing you must do is _____ .

    A. writing              

    B. reading              

    C. asking          

    D. answering

4. A clever student usually likes _____ .

    A. asking questions                    

    B answering questions

    C. finding answers                    

   D. teaching others

5. If you want to succeed, you'd better learn_____ .

    A. how to teach others                        

    B. how to teach yourself

    C. to read and write carefully              

    D. how to ask questions

单项选择题