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问题 问答题

如图所示，由AO、OB两绳挂着一物体，物体的质量为m=30kg，求：

（1）AO、0B的拉力；

（2）若AO、OB的最大承受力分别为150N、100N，则最多能挂多重的物体（g取10m/s2）？

答案

（1）O点受力如图所示；根据平衡条件及三角函数得：

FOB=mgcot60°=30×10×

3
3
=100
3
（或173）（N）

FOA=

mg
sin60°
=
30×10
3
2
=200
3
（N）

（2）cos60°=

FOB
FOA
；

 当FOA=150N时，FOB=75N＜100N，故OA绳先达到最大承受力

则由FOA=

mg
sin60°

  得：m=

FOAsin60°
g
=7.5
3
kg≈13kg

答：（1）AO的拉力为200

3
N； OB的拉力为100
3
N（173N）；

    （2）能挂物体的最大质量为13kg．

阅读理解

I was going to bed the other night when my wife told me that I had left the light on in the shed（储藏室）. She could see it from the bedroom window. As I looked for myself, I saw that there were thieves in the shed taking things. I phoned the police, but they told me that no one was in this area to help at this time, but they would send someone over as soon as they were free.

I said OK, hung up, and waited one minute, then phoned the police back, “Hello, I just called you a minute ago because there were thieves in my shed. Well, you don’t have to worry about them now because I’ve killed them all.”

Within five minutes there were six police cars in the area. Of course, they caught the thieves very quickly. One of the officers said: “I thought you said that you’d killed them!” I replied with “I thought you said there was nobody free!”

小题1:There were thieves in the        .

A．shed

B．bedroom

C．kitchen

D．garden小题2:The man        when he found the thieves.

A．caught them by himself

B．called the police at once

C．did nothing but wait

D．killed them小题3:The police said that        so they couldn’t come and help at first.

A．it was too far

B．the car was broken

C．they were all busy

D．it was too cold小题4:The police        when the man called them again.

A．found it boring

B．took it serious

C．let it go

D．have a rest小题5:The thieves were        at the end of the story.

A．lost

B．killed

C．caught

D．away
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单项选择题

在Access2003中，以下不属于窗体的功能的是（）。

A.显示和编辑数据内容

B.显示注释、说明或警告信息

C.控制应用程序的运行步骤

D.保存数据
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