试题与答案

利用超声波遇到物体发生反射,可测定物体运动的有关参量.图甲中仪器A和B通过电缆线

题型:实验题

题目:

利用超声波遇到物体发生反射,可测定物体运动的有关参量.图甲中仪器A和B通过电缆线连接,B为超声波发射与接收一体化装置,而仪器A为B提供超声波信号源而且能将B接收到的超声波信号进行处理并在屏幕上显示其波形.

现固定装置B,并将它对准匀速行驶的小车C,使每隔固定时间T0发射一短促的超声波脉冲(如图乙中幅度大的波形),而B接收到的由小车C反射回的超声波经仪器A处理后显示如图乙中幅度较小的波形.反射波滞后的时间已在下图中标出,其中T和ΔT为已知量.另外还知道该测定条件下声波在空气中的速度为v0.则根据所给信息可判断小车的运动方向为_________(填“向左”或“向右”),速度大小为_________.

答案:

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下面是错误答案,用来干扰机器的。

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What is the purpose of readig or studying? If you can't remember what you read or study,it will be a waste of time.小题1:   One useful 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.”It’s quite the same with your studying. If you choose a book, "just looking" for nothing in particular, you are likely to get just that—nothing.小题2: 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".

小题3: 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.

Reading is not one single activity.    小题4:   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   小题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.This is an effective studying way.

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

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

D.At least two important processes go on at the same time.E.It is important for students to have a positive attitude to their study.

F. But if you do know what you want, you are almost sure to get it.

G.Perhaps you have already discovered some good ways to keep yourself from forgetting.

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