问题 计算题

如图所示,质量为m的物体从倾角为θ的斜面上的A点以速度v0沿斜面上滑,由于μmgcosθ<mgsinθ,所以它滑到最高点后又滑下来,当它下滑到B点时,速度大小恰好也是v0,设物体与斜面间的动摩擦因数为μ,求AB间的距离.  

答案

解:设物体m从A点到最高点的位移为x,对此过程由动能定理得:

-(mgsinθ+μmgcosθ)·x=0-mv02  ①

对全过程由动能定理得:mgsinθ·xAB-μmgcosθ·(2x+xAB)=0 ②

由①②得:xAB

阅读理解

阅读理解。

     Once there was a boy called Dick. He was poor. His father and mother were dead and he had no

friends to help him.

     One day he heard some men talking. "I shall go to London, for London is a big city and its streets

are covered with gold (黄金). Everyone in London is very rich."

     Then Dick said. "I shall also go to London and become rich."

     Some days later. Dick saw a cart (马车) on the side of the road. He said to the man who was on

the cart, "Where are you going?" The man answered. "I'm going to London." "Will you take me to

London with you?" asked Dick. The man said ."I will."

      When Dick arrived in London, he saw that the streets were not made of gold. There were very

many houses along the side of the streets. Dick got down. and the man and the cart went away.

       Dick stood in the street. He had no house to go to, no food to eat and no friends.

l. Why did the man on the cart get to London?

A. He wanted to take Dick there        

B. He was asked to find gold there.

C. The story doesn't tell us.

2. Dick went to London because _____.

A. his parents had died    

B. he wanted to be rich     

C. London was covered with gold  

3. From this passage we can see that the man on the cart was very _____.

A. kind      

B. rich      

C. old

4. Which is not true?

A. Everyone in London is very rich.        

B. London is a big city with a lot of houses.

C. Dick didn't become rich in London.

5. This passage mainly tells us something about _____.

A. the family of Dick's      

B. A poor boy Dick        

C. the city of London

填空题