问题 问答题

如图所示,倾角为的斜面处于竖直向下的匀强电场中,在斜面上某点以初速度水平抛出一个质量为m的带正电小球,小球在电场中受到的电场力与小球所受的重力相等,地球表面重力加速度为g,设斜面足够长.问:小球经多长时间落到斜面?

答案

t=(v0tanθ)/g

分析小球受力小球做类平抛运动

a=(qE+mg)/m="2g-----------------      " ①   5分 

小球落至斜面时:x="at------------------  " ②    2分 

y=1/2at2----------------------------    ③   2分 

tanθ="y/x------------------------      " ④    2分  

由①②③④得t=(v0tanθ)/g--------------   ⑤    5分 

完形填空
完形填空。
     Peter is seven years old. He's a student of Grade One. He  1  like school. It's Sunday today. The
little boy doesn't  2  He's playing a ball. near a house,  3  grandma comes to him and begins to talk  4  
his school with   5 
    "Who is the best student   6   your class,Peter?" She asks.
     "Of course I am."Peter answers.
    "Why?"
     "In my class only I  7   answer my teacher's question.
    "   8  question?"
     "He often asks  us,'Who don't understand me?' only I put up my   9 ."
    "And who is the worst (最差的) in your class?"
     "Our,  10  is. "
    "Why?"
    "He can't answer even the easiest (最简单的) questions," peter says, "he always asks my classmates
to answer them!"
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( )2. A. go home    
( )3. A. Her        
( )4. A. With        
( )5. A. he          
( )6. A. at          
( )7. A. can't      
( )8. A. What        
( )9. A. hand        
( )10. A. classmates
B. don't        
B. go to school
B. his          
B. on          
B. her          
B. can          
B. can          
B. Which        
B. hands        
B. friend      
C. isn't      
C. go to work
C. He        
C. in        
C. him        
C. in        
C. may        
C. how        
C. head      
C. students  
D. aren't            
D. go to play a ball
D. she              
D. about            
D. his              
D. of                
D. must              
D. Why                               
D. foot              
D. teacher          
单项选择题