问题 选择题

关于位移和路程,下列说法正确的是(  )

A.质点运动的位移大小可能大于路程

B.位移和路程都是矢量

C.质点通过一段路程,位移不可能是零

D.质点运动一段时间,路程不能为零但位移可能为零

答案

A、位移的大小等于初位置与末位置之间有向线段的长度,路程是物体运动路线的长度,位移大小小于等于路程.故A错误;

B、位移是矢量,位移的方向由初位置指向末位置,路程是标量,故B错误;

C、位移取决于物体的始末位置,路程取决于物体实际运动的路径,所以质点运动一段时间,路程不能为零但位移可能为零,故C错误,D正确.

故选:D.

完形填空
完形填空。
    What is the population of China? There are more than 1.3 billion people in China. It is   1   one fifth of
the world's population. How to control the population growth is a big problem. Some people think it's   2   
to control the population growth. But I don't quite agree   3   them because where there is a will, there is
a way. 
    The question is how we could   4   it known to everyone how serious the population problems are. Our
farmland is becoming less and less to everyone. We have already got too many mouths to feed.   5   we
control the population growth, many people will die   6   hunger. Too fast population growth will be bad for
our nation. Though laws have been passed to control the population growth, in some places   7   is done to
carry out the laws. We should make people   8   that it is foolish of them to give birth to too many children.
They should no longer do what they have been doing for many years.
    We are fighting   9   too fast population growth. Yet the fighting won't end  10  everyone knows its
importance and does something for it.
( )1. A. most   
(     )2. A. possible
(     )3. A. to     
(     )4. A. let    
(     )5. A. If not 
(     )6. A. of     
(     )7. A. many   
(     )8. A. to know
(     )9. A. for    
(     )10. A. until  
B. almost     
B. necessary  
B. for        
B. make       
B. Unless     
B. about      
B. little     
B. to learn   
B. against    
B. after    
C. highly    
C. impossible   
C. with      
C. have      
C. Until     
C. in        
C. a lot     
C. know      
C. to        
C. when      
D. hardly      
D. unnecessary   
D. on            
D. bring         
D. If            
D. out of                            
D. much          
D. learning      
D. about         
D. as          
多项选择题