题干

如图所示,用两根长度相同的绝缘细线把一个质量为0.1kg的小球A悬挂到水平板的MN两点,A上带有Q=3.0×10-6C的正电荷。两线夹角为120°,两线上的拉力大小分别为F1和F2。A的正下方0.3m处放有一带等量异种电荷的小球B,B与绝缘支架的总质量为0.2kg(重力加速度取g=10m/s2;静电力常量k=9.0×109N·m2/C2,AB球可视为点电荷)则(      )

A:支架对地面的压力大小为2.0N

B:两线上的拉力大小F1=F2=1.9N

C:将B水平右移,使M、A、B在同一直线上,此时两线上的拉力大小为F1=1.225N,F2=1.0N

D:将B移到无穷远处,两线上的拉力大小F1=F2=0.866N

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答案(点此获取答案解析)

B,C

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阅读理解

    Why read, and sometimes even write poetry? That question is not difficult to answer if we change the word poetry to songs.

    I sing when I feel good. When I sing my favorite songs, I feel even better. Sometimes when I am listening to music and to the song words, I feel that it was written for me. A good song always makes me feel something. There are songs that I sing in my head between classes and songs that I want to sing when the school bell rings by the end of the day. They help me get through the day.

    They are like bright and warm colors in the middle of grays and shades. I like songs about love and friendship. The extraordinary thing is that my feelings are more special when I sing my favorite songs in English.

    I also like reading. I used to avoid poetry until an e-friend told me I should recite poems and not look up the meaning of the words. Poetry uses many difficult words and idioms, but the best thing is to just forget about them. In the beginning I felt quite strange. Now I always lock the door. Reading aloud gives you a strange feeling, but when you have some practice and fall into the rhythm, and the sounds of the words, it is really a special experience.

    I started with small poems, but now I think I most like long poems. I have different feelings with different poems. When I have had a bad day at school, I read Keats and forget everything. When I am sad I read Wordsworth by the light of a candle. When the poem is finished, I close the book and my sadness is gone.