问题 选择题

一匀强电场的电场强度E随时间t变化的图象如图所示,在该匀强电场中,有一个带电粒子在t=0时刻由静止释放,若带电粒子只受电场力作用,则下列说法中正确的是(  )

A.带电粒子只向一个方向运动

B.0~2s内,电场力做正功

C.2s末带电粒子回到原出发点

D.4s末带电粒子回到原出发点

答案

带电粒子在t=0时刻由静止释放,在0-1s内带电粒子沿着电场力方向做匀加速直线运动,

1-2s内沿原方向做匀减速直线运动,2s末速度减为零;

2-3s内沿反方向做初速度为零的匀加速直线运动,

3-4s内继续做匀减速直线运动,4s末速度减为零,回到出发点.

A、由上分析可知,带电粒子做往复运动.故A错误.

B、0~1s内电场力做正功,1~2s内电场力做负功.故B错误.

C、D,2s末带电粒子离原出发点最远,4s末带电粒子回到原出发点.故C错误,D正确.

故选D

完形填空
完形填空。
     Two friends went to a city and     1     in a big hotel. Their room was on the 56th floor,
and there was a fast lift, so they went up and down very     2     . They came back to the hotel
very late one Saturday     3     ,and the liftman said to them," The electricity (电) stopped today.
You can't    4      the lift now, " The two friends said. "We    5     to go upstairs (上楼) to our room."
     They left their coats downstairs because they were     6    , and began to climb. It took a     7    
time, but they sang some interesting songs. At 12:00, they      8    the 56th floor. Then one of them
put his hand in his pocket (口袋) and stopped. He said to    9     , "Now. I'm going to sing the most
interesting song of all. Its name is: I    10      the key to the room downstairs in my coat."
( )l. A. ate        
( )2. A. early     
( )3. A. morning   
( )4. A. climb     
( )5. A. like      
( )6. A. light     
( )7. A.short      
( )8. A. got to    
( )9. A. the liftman
( )10. A. put      
B. slept    
B. easily  
B. afternoon
B. see     
B. want    
B. beautiful
B. little  
B. went up 
B. the other
B. bought  
C. lived     
C. friendly 
C. night    
C. make     
C. have     
C. heavy    
C. long     
C. turned to
C. the worker
C. left     
D. played        
D. carefully     
D. time          
D. use           
D. start         
D. old           
D. lot           
D. walked down   
D. the businessman
D. threw         
填空题