问题 问答题

如图所示,弹簧振子在BC之间作机械振动,O点为平衡位置.请画出:

(1)弹簧振子在B点的位移s;

(2)弹簧振子在C点的加速度a的方向.

答案

(1)位移用从平衡位置到终点的有向线段表示,即可以用一根从O点到B点的有向线段表示,如图所示;

(2)在C位置时,合力指向O点,故加速度也指向O点,即指向平衡位置,如图所示.

阅读理解

阅读理解。

     请阅读下面一篇文章,并按照要求匹配信息。

      It doesn't come as a surprise to you to realize that it makes no difference what you read

or study if you can't remember it. You just waste your valuable time. 1  One dependable

aid that does help you remember what you study is to have a specific purpose or reason for

reading.

     Why does a clerk in a store go away when your reply to her offer to help is, "No, thank

you.I'm just looking."? Both you and she know that if you aren't sure what you want, you are

not likely to find it.But suppose you say instead, "Yes, thank you.I want a pair of sun glasses."

She says, "Right this way, please".

      2  If you choose a book, "just looking" for nothing in particular, you are likely to get just

that-nothing.But if you do know what you want, you are almost sure to get it.Your reasons will

vary; they will include reading or studying "to find out more about", "to understand the reasons

for" and "to find out how".Before you start to study, you say to yourself something like

this, "I want to know why Stephen Vincent Benet happened to write about America".Because

you know why you are reading or studying, you relate the information to your purpose and

remember it better.

     4 At least two important processes go on at the same time.As you read, you take in ideas

rapidly and accurately.But at the same time you express your own ideas to yourself as you react

to what you read. You have a kind of mental conversation with the author.

     This additional process of thinking about what you read includes evaluating it, relating it to

what you already know, and using it for your own purposes.  5  One part of critical reading,

as you have discovered, is distinguishing between facts and opinions.Facts can be checked

by evidence. Opinions are one's own personal reactions.Another part of critical reading is

judging sources.Still another part is drawing accurate inferences.

     A. Maybe you have already discovered some clever ways to keep yourself from forgetting.

     B. It is important for students to have a positive attitude to their study.

     C. You remember better when you know what you' re reading.

     D. In other words, a good reader is a critical reader.

     E. It's quite the same with your studying.

     F. Reading is not one single activity.

     G. This is the way it works.        

单项选择题