如图所示，物体A和B的质量分别为2kg和1kg，用跨过定滑轮的细线相_爱下问搜题

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问题选择题

如图所示，物体A和B的质量分别为2kg和1kg，用跨过定滑轮的细线相连，静止地又叠放在倾角为=30⁰的光滑斜面上，A与B间的动摩擦因数为，现有一平行于斜面向下的力F作用在物体B上，设最大静摩擦力等于滑动摩擦力，若要使物体运动，则F至少为（）（）

A．20N

B．22N

C．11N

D．17N

答案

答案：D

题目分析：分析物体A受力，要向拉动A，那么拉力T至少要等于，分析B受力如图，B受到自身重力，A的压力和A对B 的摩擦力，要把B向下滑动，那么拉力F至少为，对照答案B对。

阅读理解

读短文，选择正确答案。

My name is Betty. I live in China. I study in Shanghai No. 6 Primary School. My birthday is coming. It's in

August. On my birthday I often get up at 7: 30. I buy a lot of food with my mother in the supermarket. Usually,

I have a good time on my birthday.

In the evening, I eat dinner at 6: 00. Then I have a birthday party. At the party, we play games and eat a big

birthday cake. I eat ice cream, too. It's my favourite.

1. When is Betty's birthday?[ ]

A. In fall.

B. In winter.

2. A supermarket is a _____________.[ ]

A. store

B. playground

3. Is Betty happy on her birthday?[ ]

A. Yes, she is.

B. No, she isn't.

4. Does Betty like to eat ice cream?[ ]

A. Yes, she does.

B. No, she doesn't.

5. What do they do in her party?[ ]

A. They watch TV.

B. They play games.

问答题简答题

压缩试验中，对试样尺寸有什么要求及其理由？