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问题 单项选择题

YJV型电力电缆（）。

A.能承受机械外力作用

B.适用于管道内敷设

C.可敷设在地下

D.可承受相当大的拉力

答案

参考答案：B

完形填空
完形填空。
     I'm a student. I go to school on weekdays. I don't have   1   free time. I usually   2   six or seven hours
at school. After that I either go shopping   3   go home and study. If I have some   4  time during weekdays,
I   5  read a storybook or watch TV. But now it takes all my evenings to study   6   the final exam.
    Though I have a lot to do, I still have some free time activities. On weekends I like to go out with my
family. I also like to walk around the countryside and   7   the seasons change during spring and autumn.
I am also a   8  . I am interested in stone collecting. I like to   9   all kinds of interesting stones. In winter
I enjoy sports like skiing and skating. I'm  10  a good skier (滑雪者). In our class no one can ski better
than me.
( )1. A. too many            
( )2. A. need                
( )3. A. but                
( )4. A. busy                
( )5. A. may                 
( )6. A. with                
( )7. A. watch               
( )8. A. teenager            
( )9. A. look over         
( )10. A. real               		B. too much         
B. spend            
B. and              
B. empty            
B. have to           
B. in               
B. like              
B. volunteer            
B. look like        
B. quite          		C. much too        
C. cost            
C. so              
C. free            
C. must            
C. on              
C. hope              
C. collector            
C. look at        
C. very          		D. amny too         
D. take             
D. or               
D. funny            
D. can't                                         
D. for               
D. want                
D. leader           
D. look for       
D. pretty       
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计算题

（13分）如图所示，A、B质量分别为mA＝1kg，mB＝2kg，AB间用弹簧连接着。弹簧劲度系数k＝100N／m。轻绳一端系在A上，另一端跨过定滑轮。B为套在轻绳上的光滑圆环，另一圆环C固定在桌边，B被C挡住而静止在C上。若开始时作用在绳子另一端的拉力F为零。此时A处于静止且刚好没接触地面。现用恒定拉力F＝15N拉绳子，恰能使B离开C但不能继续上升，不计一切摩擦且弹簧没超过弹性限度，求：（g取10m／s2）

（1）B刚要离开C时A的加速度；

（2）若把拉力F改为F＝30N，则B刚要离开C时，A的加速度和速度。
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