问题 问答题

陈锋同学的家到学校本是一条在同一水平面上的直路,爱动脑的陈锋做了这样的设想:要是将从家到学校的路挖成一个“U”字形(如图所示),只要从家骑上自行车后,不用刹车也不用踩车,等车停下来就可以到达学校了。请你简要说明:

(1)陈锋同学的设想的机械能转化过程

(2)陈锋同学的设想在现实中可以实现吗? 为什么?(请根据有关物理知识说明)

答案

(1)重力势能--动能--重力势能

(2)不能实现,存在路面摩擦和空气阻力,运动过程中要克服阻力做功,一部分机械能转化为其它形式能,机械能不守恒。

阅读理解

阅读理解。

     An old woman opens her windows and looks out.What a sunny day !  But she is surprised there is a

man in the front of her garden. The old woman looks  at  him and says to  herself,  " He  is  eating grass

(草 ) . Why?"  She goes out into her garden and says to him," Are you very hungry? Why don't you go

to  work and get  some food?"The man looks at her and says,  "I don't like working. I  just  like  eating.

Now I'm hungry,  I  have nothing for my breakfast.  You see,  I'm eating grass.  Can you give me some

food ? "

     The old woman says,"Come to the back door of my house. " The man is very glad. He thinks he can

get food from the old woman.  So he  goes  with her.  The old woman opens the back door and says to

the man. " Look, the grass here is longer than that in the garden. Just enjoy it here ! "            

l. What's the man doing in the garden?He is     there .

A. working hard        

B. opening the windows

C. eating some food      

D. eating grass

2. What does the man have for breakfast?

A. Some food.            

B.Nothing.

C. Vegetables.            

D. Fruits.

3. How does the man feel when the old woman asks him to the back door?

He is       .

A. sad                    

B. sorry

C. interesting              

D. happy

4. What does the woman ask him to do?

A. She asks him to work for her.

B. She asks him to the back door and eat food.

C. She asks him to the back door and eat the grass there.

D. She gives him some food at the back door.

5. What does the man like doing?

A. He likes working.    

B. He likes dancing.

C. He likes eating.      

D. He likes singing.

单项选择题