问题 选择题

一物体做加速直线运动,依次通过A、B、C三点,AB=BC,物体在AB段的加速度为a1,所用时间为t1,在BC段的加速度为a2,所用时间为t2,且物体在B点的速度为VB=

VA+VC
2
,则(  )

A.a1=a2

B.a1>a2

C.t1=t2

D.t1>t2

答案

通过图线可以看出,两端位移相等,即图线与时间轴所围成的面积相等,可以得出BC段图线的斜率大于AB段图线的斜率,所以a1<a2

由图线可知,t1>t2.故D正确,A、B、C错误.

完形填空
完形填空。
     The day before Clara's birthday, she was very 1 . She hoped she would get lots  of   presents.  She went to her
bedroom, and began to 2 a letter to her mother. 3 the letter, she said she would like to go on a picnic and open her
presents during the picnic. Clara gave her mom the letter and her mom said, "Thanks, dear. Go to bed 4 I'll read it."
Clara went to bed with her favorite teddy bear. Her mom 5 her face and said, "Good night."
     Early next morning, Clara put on her 6 and went to the living room.  Her mom was 7 things for the picnic. After
breakfast, the family 8 their car to the park. They found a good place.   Clara unwrapped her presents. There were
beautiful skirts, dolls and books. Finally, Mom took out the last present. It was a 9 box. Clara opened the box and
found a pot. A lovely fish was swimming in it. Clara was so happy. Now, she still remembers that birthday 10 .
( )1. A. surprised  
( )2. A. send      
( )3. A. On        
( )4. A. but        
( )5. A. saw        
( )6. A. bags      
( )7. A. making    
( )8. A. drove      
( )9. A. broken    
( )10.A. right now  
B. pleased  
B. draw      
B. In        
B. so        
B. washed    
B. clothes  
B. planting  
B. mended    
B. ugly      
B. at first  
C. relaxed      
C. write        
C. From        
C. and          
C. forgot      
C. glasses      
C. borrowing    
C. stopped      
C. bright      
C. all the time
D. worried      
D. find        
D. Before      
D. or          
D. kissed      
D. gloves      
D. preparing    
D. cleaned      
D. pretty      
D. just now    
单项选择题