如图1所示,一个质量m=0.1 kg的正方形金属框总电阻R=0.5 Ω,金属框放

题型:计算题

问题:

如图1所示,一个质量m=0.1 kg的正方形金属框总电阻R=0.5 Ω,金属框放在表面绝缘的斜面AA′B′B的顶端(金属框上边与AA′重合),自静止开始沿斜面下滑,下滑过程中穿过一段边界与斜面底边BB′平行、宽度为d的匀强磁场后滑至斜面底端(金属框下边与BB′重合),设金属框在下滑过程中的速度为v,与此对应的位移为x,那么v2-x图象如图2所示,已知匀强磁场方向垂直斜面向上,金属框与斜面间的动摩擦因数μ=0.5,取g=10 m/s2,sin53°=0.8,cos53°=0.6。

(1)根据v2-x图象所提供的信息,计算出金属框从斜面顶端滑至底端所需的时间t;

(2)求出斜面AA′B′B的倾斜角θ;

(3)求匀强磁场的磁感应强度B的大小。

考点:牛顿运动定律的应用匀变速直线运动规律的应用共点力的平衡
题型:计算题

阅读理解。

     When you see the girl for the first time, you may think she is a boy. She is very outgoing (外向). Who is

she? Wang Meng, the Chinese top skater.

     On the evening of February 26th, 2010, Wang Meng first got to the finishing line in 1 minute and 29.213

seconds in the women's 1000 meters short track speed skating final (短道速滑决赛) at the Vancouer Olympic

Winter Games (温哥华冬奥会). After she succeeded in the 500-meter and 3000-meter races, she won her

third gold medal this time. With this one China won four gold medals in the women's short track speed skating.

That helped China first win the team gold medal in Winter Olympics history.

     Just before the final race Wang Meng caught a bad cold and coughed terribly. With the words of "You can,

you can do!" she won at last. She said, "I really feel these three gold medals belong to my team, to China. It

was with the help of my team that I won the prize."

     Though Wang Meng is only twenty-four, she has been the most successful Chinese skater. Chinese are

proud of her and her team. We hope she will be faster in Sochi Olympics in 2014.

1. China won ____ gold medals in the women's short track speed skating.

A. 2

B. 3

C. 4

D. 5

2. It took Wang Meng 1 minutes and 29.213 seconds to finish the ____ short track speed skating final.

A. women's 1000

B. men's 1000

C. women's 500

D. men's 500

3. In Wang Meng's opinion, ____ made her win the prize at last.

A. a strong body

B. a bad cold

C. her team's help

D. much exercise

4. Which of the following is NOT true according to the passage?

A. Wang Meng is very outgoing like a boy.

B. Wang Meng is the most successful Chinese skater.

C. Chinese people are proud of Wang Meng and her team.

D. China has got the team gold medal twice in Winter Olympics history.

题型:计算题

污水处理厂必须设在集中给水水源的下游,并要求在城市夏季最( )频率风向的上风侧,并与城市、工厂和生活区有( )m以上距离,且要设防护带。

A.小;200
B.大;200
C.小;300
D.大;300

题型:计算题

‘我国三峡电站在“竞价上网”前采取()方法制定上网电价。

A.还本付息电价

B.招标定价

C.以受电省电力市场平均电价倒推定价

D.经营期电价

题型:计算题

1878年,征战四方的日本海军因食用精米白面,约有三分之一的人得了一种疾病,病人全身浮肿、肌肉疼痛、四肢无力,脚肿得象酒瓮。这种病是由于食物中缺少(   )引起的。

A.维生素A

B.维生素 B1

C.维生素C

D.维生素D

题型:计算题

“Humans should not try to avoid stress any more than they would shun food, love or exercise.” said Dr. Hans Selye, the first physician to document the effects of stress on the body. While here’s no question that continuous stress is harmful, several studies suggest that challenging situations in which you’re able to rise to the occasion can be good for you.

  In a 2001 study of 158 hospital nurses, those who faced considerable work demands but coped with(设法处理) the challenge were more likely to say they were in good health than those who felt they couldn’t get the job done.

  Stress that you can manage may also boost immune(免疫的) function. In a study at the Academic Center for Dentistry in Amsterdam, researchers put volunteers through two stressful experiences. In the first, a timed task that required memorizing a list followed by a short test, subjects believed they had control over the outcome. In the second, they weren’t in control: They had to sit through a gory(血淋淋的) video on surgical procedures. Those who did go on the memory test had an increase in levels of immunoglobulin A, an antibody that's the body’s first line of defense against germs. The video-watchers experienced a downturn in the antibody.

  Stress prompts the body to produce certain stress hormones(荷尔蒙). In short bursts these hormones have a positive effect, including improved memory function. “They can help nerve cells handle information and put it into storage,” says Dr. Bruce McEwen of Rockefeller University in New York. But in the long run these hormones can have a harmful effect on the body and brain.

“Sustained stress is not good for you,” says Richard Morimoto, a researcher at Northwestern University in Illinois studying the effects of stress on longevity(长寿), “It’s the occasional burst of stress or brief exposure to stress that could be protective.”

小题1:The passage is mainly about ________.

A.the benefits of manageable stress

B.how to avoid stressful situations

C.how to cope with stress effectively

D.the effects of stress hormones on memory小题2: The underlined word “shun” (Line 1, Para.1) most probably means________.

A.cut down on

B.stay away from

C.run out of

D.put up with小题3: We can conclude from the study of the 158 nurses in 2001 that ________.

A.people under stress tend to have a poor memory

B.people who can’t get their job done experience more stress

C.doing challenging work may be good for one’s health

D.stress will weaken the body’s defense against germs小题4:Dr. Bruce McEwen of Rockefeller University believes that ________.

A.a person’s memory is determined by the level of hormones in his body

B.stress hormones have lasting positive effects on the brain

C.short bursts of stress hormones enhance memory function

D.a person’s memory improves with continued experience of stress

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