问题 选择题

关于机械振动和机械波,下列说法正确的是:( )

A.共振是受迫振动的一种特殊情况

B.机械波传播过程中,介质中的单个质点的能量是守恒的

C.当障碍物的尺寸比波长大时,就不能观察到明显的波的衍射现象

D.如右图所示,频率恒定的声源按路线a→b→c→d→a逆时针做匀速圆周运动,观察者在圆心不动,则观察者接收到的声波频率始终与声源频率相同

答案

AD

题目分析:物体在周期性驱动力作用下的振动叫受迫振动,当驱动力的周期等于物体的固有周期时,振幅最大,成为共振,所以A正确;机械波在传播的过程中不仅传播振动形式同时也传播能量,这种能量传递是通过质点间的相互作用力做功来实现的,所以B错误;当障碍物的尺寸与波长相差不多或比波长小时能观察到明显的衍射现象,相差不多可以不波长略大一点,所以C错误;生源在运动过程中与观察者间的距离没有发生变化,所以观察者接受的声波频率始终与声源频率相同,所以D 正确。

阅读理解

阅读理解。

Dear Kitty,

      News! We have a new flat! The rooms are small, but they are comfortable. There are more rooms

here than in our old flat. This is good because now I have my own room. In the old flat, I shared with

my sister.

     My bedroom is my favourite room in our flat. I can be alone in it. I can read or draw. I can listen to

my radio or play CDs. I can play games on my computer and send e-mails to my friends.

     My second favorite room is the kitchen. I love helping my mother cook our meals. She is a very good

cook. She is teaching me how to make many different kinds of dishes. She lived in Morocco when she

was a girl, and she can cook Moroccan food. It's very delicious. That's all for now. Write soon and tell

me about your home. Please get on the Internet so that we can send e-mails to each other.

     All good wishes!

                                                                                                                                         Anna

1. What is the main idea of this article?

A. Anna told Kitty something about her family's new flat.

B. Kitty lives with her family in America.

C. Anna likes her bedroom .

D. Anna's mother is teaching her Moroccan food.

2. What is the difference between the old flat and the new one?

A. The rooms in the new flat are big.

B. The rooms in the old flat were smaller.

C. There are more rooms in the new flat.

D. There were more rooms in the old flat.

3. Why is Anna very pleased with the new flat?

A. Because she has to share a room.        

B. Because she has a big room.

C. Because she has a small room.          

D. Because she has her own room.

4. Which room is Anna's favorite?

A. The living room.  

B. The kitchen.  

C. The bedroom.

D. The bathroom.

5. What does Anna do in the kitchen?

A. She helps her mother cook their meals.      

B. She plays computer games.

C. She teaches her mother how to cook.        

D. She reads about Moroccan food.

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