水平导轨AB固定在支架CD上,其形状、尺寸如图所示。导轨与支架的总质量M=4kg

题型:计算题

问题:

水平导轨AB固定在支架CD上,其形状、尺寸如图所示。导轨与支架的总质量M=4kg,其重心在O点,它只能绕支架C点且垂直于纸面的水平轴转动。质量m=1kg的小铁块静止于水平导轨AB的A端,现受到水平拉力F=2.5N的作用。已知小铁块和导轨之间的动摩擦因数μ=0.2。g取10m/s2,求:

(1)小铁块刚开始运动时的加速度大小?

(2)小铁块运动到离A端多远时,支架将要开始翻转?

(3)若在小铁块运动的过程中,支架始终保持静止,则拉力F作用的最长时间为多少?

考点:牛顿运动定律的应用力矩的平衡
题型:计算题

根据短文内容,从短文后的选项中选出能填入空白处的最佳选项,选项中有两项为多余选项。

Choosing to Study Overseas

Every year, thousands of students choose to study in another country for a semester, the summer, or a year. Studying overseas can be an exciting experience for many people.

  小题1:  

Living in another country can help you to learn a language, and about another culture.    小题2:  

Overseas study may also look good on your future resume. Many companies today want employees who speak a second language, or have experienced living or working in another country.

Making the right choice

Once you decide to study overseas, you have to make some choices. To choose the right country or school. Ask yourself: Where do I want to go and why? How much do I want to pay?    小题3:   Do I want to live with a host family, with roommates, or alone?

Getting ready to go

Get your passport and visa early!    小题4:   Learn about the money. Bring some of it, and a credit card, with you.

Once you are there

After the first few weeks overseas, many students will feel a little homesick. They may miss their family, friends, and familiar ways of doing things.    小题5:   When you feel sad or homesick, try to talk to others, or write about your feelings in a notebook.

A.Why do it?

B.You should improve your mother tongue before you go.

C.Large number of students can’t afford to study overseas.

D.How long do I want to study overseas?E. Remember that it takes time to get used to a new place, school, and culture.

F. You will see the world in a new way, and learn more about yourself.

G. Before you go, learn some of the language, and read about some common customs in your host country.

题型:计算题

下图示意4个国家人口的性别年龄构成。读图完成1~2题:

1.图示四国中人口自然增长率最高的是[ ]

A.①  

B.②  

C.③  

D.④

2.图示四国中30~39岁人口数量从少到多依次是[ ]

A.①③④②  

B.②④③①

C.④②③①  

D.①②③④

题型:计算题

农民,2周前出现腹泻,为果酱样大便,日达7~10次,伴右下腹部压痛,无发热,无里急后重,大便常规发现夏-雷晶体,诊断是()

A.急性菌痢普通型

B.霍乱

C.病毒性肠炎

D.普通型阿米巴痢疾

E.伤寒

题型:计算题

桡神经损伤可出现在()。

A.肱骨髁上骨折

B.肱骨中上1/3骨折

C.肱骨干骨折

D.肱骨中下1/3骨折

E.肱骨髁间粉碎性骨折

题型:计算题

陈启沅是著名的民族企业家,在1874年创办了继昌隆缫丝厂,1881年底,他把缫丝厂迁到()

A.广州

B.深圳

C.香港

D.澳门

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