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在如图所示竖直平面坐标系内，在第四象限内存在垂直纸面向里的匀强磁场和水平方向 的匀强电场，磁感应强度为B，电场强度E1的大小和方向未知．质量为m、带电量为q的 液滴从p点沿图中虚线匀速运动到原点o进入第二象限，在第二象限内存在水平向右的 匀强电场，其场强大小为E2．已知P点坐标为（4L，-3L），重力加速度为g．求：

（1）E1的方向和大小．

（2）液滴在第四象限匀速运动的速度大小．

（3）液滴通过0点后再次通过x轴时的坐标．

答案

（1）带电粒子由P运动到O的过程中，粒子受到重力、电场力、洛伦兹力三个力作用，如图所示．故 粒子带负电，电场方向水平向右．

解得：E1=

3mg
4q
．

（2）

mg
qvB
=
4L
5L
，解得v=
5mg
4qB
．

（3）液滴进入第二象限后，将速度沿坐标轴分解

vx=

4
5
v=
mg
qB
   vy=
3
5
v=
3mg
4qB

液滴沿x轴负方向做匀加速直线运动，沿竖直方向上做竖直上抛运动

t=

2vy
g
=
3m
2qB
．

水平方向上位移大小x=vxt+

1
2
qE2
m
t2=
3m2g
2q2B2
+
9mE2
8qB2

坐标为（-

3m2g
2q2B2
-
9mE2
8qB2
，0）．

答：（1）E1的方向水平向右，大小为E1=

3mg
4q
．

（2）液滴在第四象限匀速运动的速度大小为

5mg
4qB
．

（3）液滴通过0点后再次通过x轴时的坐标为（-

3m2g
2q2B2
-
9mE2
8qB2
，0）．

材料分析题

自然资源是人类生存发展的基础。几千年的文明史是人类不断地认识、开发和利用自然资源的历史，也是人与自然资源的矛盾不断加深的历史。在传统农业社会，存在着人口与土地等资源的矛盾。随着工业化进程的加快及人口数量的增加，人口与矿产等资源的矛盾又进一步凸显出来。人口膨胀与自然资源短缺的矛盾，已经威胁到人类的生存。要树立人类的资源危机意识，促进人与自然关系的和谐发展。

结合材料，从认识论角度分析人与自然资源矛盾的变化，并从认识论角度就当前人与自然资源的矛盾提出解决思路。

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     To master a language one must be able to speak and understand the spoken language as well as to
read and write.Lenin and his wife Krupskaya_1_a long English book into Russian.But when they went
to England in 1902, _2_people couldn't understand a word they said and they couldn't understand_3_
was said to them.
     These days more and more foreigners are coming to China and_4_Chinese are going out to foreign
countries to work or study._5_the spoken language is becoming more and more important.
     Speaking, of course, can't go without_6_.If you want to pronounce a word_7_, first you must hear it
correctly.If you don't listen carefully, you'll find it difficult or even_8_to understand the native speakers.
     Well, what about writing?Like speaking, it's to_9_ideas.People generally use shorter words and
shorter sentences in their writing.The important thing is to make your idea  10   in your head and then to
write it in clear lively language.
     Chinese students read far too slowly.If you read fast, you  11   better.If you read too slowly, by the
time you have reached the end of a page you have forgotten what the   12   is about.When you  13   
 new words, don't look them up in the dictionary.Guess the meaning from the  14   .You may not guess
quite correctly the first time, but as new words   15   again and again in different contexts, their meaning
will become clearer and clearer.If you look up every word, you'll never  16    a book.
     Students of a foreign language need a  17   knowledge, the knowledge of the life, history and
geography of the people whose 18   they are studying.They should study these subjects in the foreign
language, not only in translation.In this way one 19   kill two birds with one stone:learn a foreign language
and 20   some knowledge of the foreign country at the same time.
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( )19. A. should      
( )20. A. bring       		B. kept      
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D. front        
D. put down    
D. topic        
D. come up      
D. read        
D. common      
D. culture      
D. shall        
D. get          
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