问题 计算题

如图所示,两根电阻不计,间距为的平行金属导轨,一端接有阻值为R的电阻,导轨上垂直搁置一根质量为m.电阻为r的金属棒,整个装置处于竖直向上磁感强度为B的匀强磁场中.现给金属棒施一冲量,使它以初速向左滑行.设棒与导轨间的动摩擦因数为,金属棒从开始运动到停止的整个过程中,通过电阻R的电量为q.求:(导轨足够长)

 (1)金属棒沿导轨滑行的距离;

(2)在运动的整个过程中消耗的电能.

答案

1)设滑行的距离为L

由法拉第电磁感应有  ①(2分)

 而由电流定义有            ②(2分)

 由闭合电路的欧姆定律得       ③(2分)

  由①②③解得 得  ④(2分)

 (2)由功能原理得   ⑤(3分)

        而   ⑥(3分)

       ∴    ⑦(2分)

问答题
阅读理解

阅读理解

     Betty and Harold have been married for years.But one thing still puzzles old Harold.How is it that he

can leave Betty and her friend Joan sitting on the sofa,talking,go out to a ballgame,come back three and a

half hours later,and they're still sitting on the sofa?Talking?

     What in the world,Harold wonders,do they have to talk about?

     Betty shrugs.Talk?We're friends.

     Researching this matter called friendship,psychologist Lilian Rubin spent two years interviewing more

than two hundred women and men.No matter what their age,their job,their sex,the results were completely clear:women have more friendships than men,and the difference in the content and the quality of those

friendships is "marked and unmistakable."

     More than two-thirds of the single men Rubin interviewed could not name a best friend.Those who

could were likely to name a woman.Yet three-quarters of the single women had no problem naming a best friend,and almost always it was a woman.More married men than women named their wife/husband as a

best friend,most trusted person,or the one they would turn to in time of emotional distress(感情危机).

"Most women,"says Rubin,"identified at least one,usually more,trusted friends to whom they could turn in a troubled moment,and they spoke openly about the importance of these relationships in their lives."

"In general,"writes Rubin in her new book,"women's friendships with each other rest on shared emotions

and support,but men's relationships are marked by shared activities."For the most part,Rubin says,

interactions(交往)between men are emotionally controlled-a good fit with  the social requirements of

"manly behavior."

    "Even when a man is said to be a best friend,"Robin writes,"the two share little about their innermost

feelings.Whereas a woman's closest female friend might be the first to tell her to leave a failing marriage, it

wasn't unusual to hear a man say he didn't know his friend's marriage was in serious trouble until he

appeared one night asking if he could sleep on the sofa."

1.What old Harold cannot understand or explain is the fact that_____.

A.he is treated as an outsider rather than a husband

B.women show little interest in ballgames

C.women have so much to share

D.he finds his wife difficult to talk to

2.Rubin's study shows that for emotional support a married woman is more likely to  turn to _____.

A.a male friend   

B.her parents   

C.a female friend

D.her husband

3.According to the text,which type of behavior is NOT expected of a man by society?

A.Ending his marriage without good reason.

B.Complaining about his marriage trouble.

C.Spending too much time with his friends.

D.Going out to ballgames too often.

4.Which of the following statements is best supported by the last paragraph?

A.Women are more serious than men about marriage.

B.Men keep their innermost feelings to themselves.

C.Men often take sudden action to end their marriage.

D.Women depend on others in making decisions.

5.The research done by psychologist Rubin centers around_____.

A.friendships of men and women

B.happy and successful marriages

C.emotional problems in marriage

D.interactions between men and women