一个质量为M的箱子放在水平地面上,箱内用长为L的细线栓一质量为m的小球,线的另一

题型:选择题

问题:

一个质量为M的箱子放在水平地面上,箱内用长为L的细线栓一质量为m的小球,线的另一端栓在箱子的顶板上,现把细线和球拉到与竖直方向成θ角处从静止自由释放,当球摆到最低点时,地面受到的压力为

[ ]

A.Mg(2-cosθ)

B.Mg+mg(1-cosθ)

C.(M+m)g        

D.Mg+mg(3-2cosθ)

考点:单摆的回复力
题型:选择题

阅读理解。

Dear Nancy,

         How are you? Now I want to tell something interesting. Last week we

had a trip to Mount Tai. On Tuesday we went to Taian by bus, a city at the

foot of the mountain. We had a good rest at a hotel. At about one o'clock

early the next morning, we began to climb the mountain. It took us about

four hours and a half to get to the top. The mountain is covered (覆盖) with

trees. I didn't see such a beautiful place before.

         "Look! The sun is going to rise!" my friend Lim shouted.

         We all turned to the east and watched. Soon half of the sky because

white, and a big, red ball was rising slowly. A few minutes later, the sky

became bright(明亮的).

         We stayed on the top and had a good time. After lunch we started going down.

We got to the tour hotel at about four in the afternoon. Though we

were tired, we were very happy. We came back to school the next day.

         Thank you very much for your last letter and the beautiful postcards.

Hope to hear from you soon.

                                                                                                        Yours

                                                                                                        Wu Tong    

1. The letter is from ___________to ___________.

A. Wu Tong, Nancy  

B. Nancy, Wu Tong  

C. Lim, Wu Tong  

D. Nancy, Lim

2. How did Wu Tong go to Taian?

A. On foot.          

B. By bus.          

C. By taxi.        

D. By bike.

3. When did Wu Tong reach the top of the mountain?

A.At about 1:00 pm.  

B. At about 4:00 am.  

C. At about 4:30 pm.

D. At about 5:30 am

4. The word "rise" means "__________" in Chinese.

A.赶制          

B.成功            

C.上升              

D.冲击

5. From the letter we may know _______________.

A. after supper they started to go down.    

B. they got to the tour hotel the next day

C. Nancy sent some postcards to Wu Tong  

D. Nancy had a great time in Mount Tai

题型:选择题

生活处处有化学,下列说法或做法中,不正确的是

A.海鲜在夏天容易腐烂变质:建议用甲醛溶液(福尔马林)浸泡海鲜防腐

B.被蚁虫叮咬后在人的皮肤内会分泌出蚁酸,可涂一些含NH3•H2O的药水减轻痛痒

C.硝酸钾属于复合肥,它能使植物生长,增强抗病虫害和抗倒伏能力

D.儿童患佝偻病是因为体内缺乏元素钙

题型:选择题

检测BJP的确证试验是 ()

A.热沉淀法

B.对甲苯磺酸法

C.免疫速率散射浊度法

D.酶免疫分析法

E.免疫固定电泳法

题型:选择题

当混凝土强度达到设计强度的()%,即可进行起吊工作。

A、60

B、70

C、90

D、100

题型:选择题

采用范成法用标准齿条型刀具加工标准齿轮时,其刀具的()与轮坯分度圆之间作纯滚动。

A.中线

B.齿根线

C.齿顶线

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