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问题 选择题

两个质量不同的小球用长度不等的细线栓在同一点，并在同一水平面内做匀速圆周运动，则它们运动的（　　）

A．周期相同

B．线速度相同

C．向心力相同

D．向心加速度相同

答案

对其中一个小球受力分析，如图，受重力，绳子的拉力，由于小球做匀速圆周运动，故合力提供向心力；

将重力与拉力合成，合力指向圆心，由几何关系得，合力：F=mgtanθ ①；

由向心力公式得到，F=mω2r ②；

设绳子与悬挂点间的高度差为h，由几何关系，得：r=htanθ ③；

由①②③三式得，ω=

g
h
，与绳子的长度和转动半径无关，即角速度相等．

A、因为T=

2π
ω
，角速度相等，则周期相同．故A正确．

B、根据v=rω知，两球做圆周运动的半径不同，则线速度不同．故B错误．

C、合力提供向心力，因为合力F=mgtanθ，细绳与竖直方向的夹角不同，则合力不同，向心力不同．故C错误．

D、根据a=rω2知，半径不同，则向心加速度不同．故D错误．

故选：A．

填空题

Part 4


Questions 26-45


·Read the following passage and choose the best word for each space.
·For questions 26-45, mark one letter A, B, C or D on the Answer Sheet.
During the past ten years (26) attention has been given to "telling it like it is". My impression is that this devotion to (27) one’s mind has more often led to hurt feelings and ruined relationships than (28) great joy.
I think we generally agree that never expressing real feelings and (29) all less-than-lovely thoughts about each other always leads to constructive communication. It’s a great (30) to allow ourselves to admit our human weaknesses and pursue more honest relationships with others. (31) we need to keep a balance between telling it all and telling nothing.
Recently I received a letter from a mother who had been (32) by her son to attend a weekend meeting with him. Under pressure from the group, her defenses cracked and she heard herself (33) her son for the first time that he (34) an accident—that she hadn’t been planning to have a child. He (35) told her that he couldn’t recall a single day in his childhood that he’d been happy. We cried and (36) ; I thought telling the truth had been good for us. But the trouble is, it wasn’t the whole truth. By the time Tommy was born I did want him, and at (37) he was happy. Ever since that day, we (38) . by some terrible feelings we exchanged. I must admit I’ve (39) the conclusion that some things are better left uncovered. Honesty is a fine policy, but we need a new sense of (40) . Disclosing is not a solution to every problem (41) even an end in itself. It’s useful under some circumstances and terribly hurtful under (42) . It’s a good idea, I think, to bite your (43) for ten or fifteen minutes before saying what’s (44) your mind. Try to decide whether it’s going to open up new and better ways of communication or (45) wounds that may never heal.

A．a great deal of

B．a large number of

C．many

D．many a
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单项选择题

已合作三年以上经营管理能力强、信用记录良好的担保公司在各行社提供的融资性担保责任余额不得超过其净资产的（）倍。

A、5

B、10

C、15

D、20
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