问题 填空题

小明是学校的升旗手,他将一面国旗在国歌声中匀速升到旗杆顶端。请问:(1)旗杆顶端装有定滑轮,利用它来升国旗,目的是改变__________________;(2)国旗匀速上升过程中国旗的动能______,重力势能_____机械能_____。(填变大、变小、不变)

答案

施力方向,不变,变大,变大

题目分析:首先要明确旗杆顶端的滑轮是定滑轮,根据定滑轮本质是等臂杠杆以及定滑轮的工作特点即可判断;重力势能与物体的质量和高度有关,质量越大,高度越高,重力势能就会越大.国旗杆上的滑轮为定滑轮,所以利用它来升国旗,可以改变改变施加力的方向;由于质量不变,速度不变,所以动能不变,机械能等于动能与势能之和,所以机械能变大。

点评:定滑轮实质是一个等臂杠杆,不省力,但可改变用力的方向.

完形填空
完形填空。
     The town I live in is about to put cameras at all traffic lights to catch people who run red lights.
It    1     me of how many people I've seen who take the yellow light as a    2     to go faster.I also
can't understand why people don't move when the traffic light has  turned  green. Above all, there
are those   3       situations in which someone doesn't even      4   that the light turns red, and just keeps
going.That is why so many   5  happen! All these situations make me   6     the purpose of traffic lights.
     7   , it's even more frightening to imagine letting people make their own decisions at   __8   crossroads.Do the biggest cars get to go first? Who decides who goes next? So I guess I do like the idea of a
system to 9   traffic.And I'll do my best to   10   the traffic rules: to go, to be cautious, and to stop
when I'm   11     to.
      It occurs to me that my   12      have done much the same for me    13    teaching me how to live.
They have given me many   14   lights: to get along well with others, to listen and talk to them, to help
others, and to   15    with joy and purpose.They have also given me some red lights   16   my life goes
astray(误入歧途): not to be greedy, to keep my temper, and to control my desires.And there    17    
 
  have been some yellow caution lights: to watch how much I drink, to keep control of my behavior, and
to 18   school  regularly and work hard.
      If I obey these rules, my life will be as   19   as it can be.Just as I'm wise to pay attention to the
traffic lights  when I'm walking across the street, I'm wise to pay attention to the"   20   signals" given to
me by my parents.
( )1.A.suggests      
( )2.A.sight        
( )3.A.instant      
( )4.A.notice        
( )5.A.events        
( )6.A.think of      
( )7.A.Besides      
( )8.A.noisy        
( )9.A.control      
( )10.A.learn        
( )11.A.supposed    
( )12.A.teachers    
( )13.A.in charge of
( )14.A.safe        
( )15.A.live        
( )16.A.unless      
( )17.A.still        
( )18.A.start        
( )19.A.good        
( )20.A.traffic      
B.informs    
B.signal      
B.exciting    
B.sense      
B.problems    
B.wonder about
B.Anyway      
B.narrow      
B.direct      
B.obey        
B.used        
B.friends    
B.in face of  
B.green      
B.share      
B.when        
B.even        
B.attend      
B.colorful    
B.light      
C.reminds    
C.message    
C.dangerous  
C.remember  
C.situations
C.care for  
C.Instead    
C.crowded    
C.improve    
C.protect    
C.devoted    
C.leaders    
C.in terms of
C.beneficial
C.work      
C.before    
C.only      
C.leave      
C.meaningful
C.life      
D.warns      
D.switch      
D.cautious    
D.feel        
D.accidents  
D.worry about
D.However    
D.key        
D.serve      
D.carry      
D.delighted  
D.parents    
D.in danger of
D.helpful    
D.communicate
D.till        
D.also        
D.miss        
D.healthy    
D.confidence  
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