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问题 选择题

如图所示，一个箱子中放有一物体，已知静止时物理对下底面的压力等于物体的重力，且物体与箱子上表面刚好接触．现将箱子以初速度v0竖直向上抛出，已知箱子所受空气阻力与箱子运动的速率成正比，且运动过程中始终保持图示姿态．则下列说法正确的是（　　）

A．上升过程中，物体对箱子的下底面有压力，且压力越来越小

B．上升过程中，物体对箱子的上底面有压力，且压力越来越大

C．下降过程中，物体对箱子的下底面有压力，且压力可能越来越大

D．下降过程中，物体对箱子的上底面有压力，且压力可能越来越小

答案

对箱子和物体整体受力分析，如图所示：

由牛顿第二定律可知，Mg+kv=Ma，则a=g+

kv
M

又整体向上做减速运动v减小，所以a减小；

再对物体单独受力分析：因a＞g，所以物体受到箱子上底向下的弹力FN，

由牛顿第二定律可知，

mg+FN=ma，则FN=ma-mg，而a减小，则FN减小，所以上升过程中物体对箱子上底面有压力且压力越来越小；

同理，当箱子和物体加速下降时，物体对箱子下底面有压力且压力越来越大，当Mg=kv后，箱子匀速下降，此时物体对箱子下底面压力等于它的重力mg，故C正确．

故选C

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     For 52 years my father got up every morning at 5?30 a. m., except Sunday, and went to work.I__1__
saw my father home from work ill.He had no hobbies, __2__taking care of his family.
     For 22 years, __3__I left home for college, my father__4__me every Sunday at 9?00 a. m..He was
always interested in my__5__, or how my family was doing, and I never once heard him__6__about his
lot (生活状况) in life.The calls even came when he and my mother were in other states.
     Nine years ago when I__7__my first house, my father,67 years old, spent three days__8__my house.
He would not__9__me to pay someone to have it done.All he __10__was a cup of tea, a paint brush
and to talk to him.But I was too__11__.I had a law practice to run, and I could not take__12__to hold
the brush, or talk to my father.__13__things happened several times later.
     The morning on Sunday.January 16,1996, my father telephoned me__14__, this time from my sister's
home in Florida.But the__15__came again at 4?40 p. m.that day.My father was in the__16__in Florida
with an aneurysm (动脉瘤). I got on an airplane__17__, and on the way, I__18__of all the times I had
not taken the time to talk to my father.I determined that when I arrived, I would__19__for the lost time,
and have a nice long talk with him.
     I arrived in Florida at 11?30 p. m., my father had__20__at 9?12 p. m..This time it was he who did
not have time to talk, or to wait for me.
( )1. A. ever      
( )2. A. other than  
( )3. A. because    
( )4. A. visited      
( )5. A. work        
( )6. A. worry      
( )7. A. built        
( )8. A. repairing    
( )9. A. teach        
( )10．A. asked    
( )11. A. smart  
( )12．A. practice  
( )13．A. Different  
( )14．A. as usual    
( )15．A. call  
( )16．A. church  
( )17．A. immediately
( )18．A. heard  
( )19．A. take up  
( )20．A. started out  		B. never          
B. rather than    
B. before          
B. praised        
B. life            
B. care            
B. found          
B. painting        
B. advise          
B. kept            
B. upset          
B. task            
B. Similar        
B. in pain        
B. moment          
B. school          
B. happily        
B. spoke          
B. make up        
B. given in        		C. always      
C. more than    
C. although      
C. telephoned    
C. study        
C. talk          
C. purchased    
C. cleaning      
C. force          
C. ordered  
C. busy  
C. tea  
C. Funny  
C. casually  
C. situation
C. home  
C. gradually  
C. thought  
C. turn up  
C. passed away  		D. often        
D. or rather    
D. since        
D. met          
D. plan        
D. look        
D. sold        
D. decorating  
D. allow        
D. served      
D. tired        
D. time        
D. Strange      
D. finally      
D. scene        
D. hospital    
D. carefully    
D. demanded    
D. put up      
D. come back    
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单项选择题

在股权投资基金的募集阶段，基金管理人主要通过（）等材料与投资者进行互动交流。

Ⅰ.基金合同

Ⅱ.基金招募说明书

Ⅲ.风险揭示书

Ⅳ.风险调查问卷

A.Ⅰ、Ⅱ、Ⅲ

B.Ⅱ、Ⅲ、Ⅳ.

C.Ⅰ、Ⅱ、Ⅳ

D.Ⅰ、Ⅱ、Ⅲ、Ⅳ
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