如图所示,两根粗细均匀的金属杆AB和CD的长度均为L,电阻均为R,质量分别为3m

题型:计算题

问题:

如图所示,两根粗细均匀的金属杆AB和CD的长度均为L,电阻均为R,质量分别为3m和m,用两根等长的、质量和电阻均不计的、不可伸长的柔软导线将它们连成闭合回路,悬跨在绝缘的、水平光滑的圆棒两侧,AB和CD处于水平。在金属杆AB的下方有水平匀强磁场,磁感强度的大小为B,方向与回路平面垂直,此时CD处于磁场中。现从静止开始释放金属杆AB,经过一段时间(AB、CD始终水平),在AB即将进入磁场的上边界时,其加速度为零,此时金属杆CD还处于磁场中,在此过程中金属杆AB上产生的焦耳热为Q. 重力加速度为g,试求:

(1)金属杆AB即将进入磁场上边界时的速度v1.

(2)在此过程中金属杆CD移动的距离h和系统机械能减少量.

(3)设金属杆AB在磁场中运动的速度为v2,通过计算说明v2大小的可能范围.(设CD始终在磁场中运动)

考点:共点力的平衡
题型:计算题

New rules and behavior standards(行为规范)for middle school students came out in March .Middle school is going to use a new way to decide who will be the top students. The best students won’t only have marks. They will also be kids who don’t dye(染)their hair, smoke or drink. The following are some of the new rules.

Tell the truth.Have you ever copied someone else’s work in an exam? Don’t do it again! That’s not something an honest student should do. If you have played computer games for two hours in your room, don’t tell your parents you have done your homework.

Do more at school. Good students love animals and care for other people. April is Bird-Loving Month in China. Is your school doing anything to celebrate? 

You should join! That way, you can learn more about animals and how to protect them. When more people work together, it makes it more fun for everyone.Have you ever quarreled with your teammates when your basketball team lost? Only working together can make your team stronger. Be friendly to the people you are with. Try to think of others, not only yourself.

Be open to new ideas. Have you ever thought that people could live on the moon? Maybe you’ll discover EarthII some day. Don’t look down on new ideas。 Everyone’s new ideas are important . You should welcome them, because new ideas make life better and easier for everyone.

Protect yourself. Have someone ever taken money from one of your classmates? Don’t let it happen to you . If  you have to go home late. You should take care of yourself and let your parents know.

Use the Internet carefully: The Internet can be very useful for your studies. But some thinks on the Internet aren’t for kids, so try to look at Web pages that are good for you. You can use the Web for fun or homework.

(  )57.When did the new rules come out ?

A. Last year.     B. Last week.    C. Last   month.

(  )58.  Do you have to tell your parents if you have played computer games instead of doing your homework according to the new rule?

A. Yes, I do.   B. There’s no need to do that.   C No, I don’t.   

(  )59. What should you do if you can’t get home on time according to the new rule?

A. I wouldn’t say anything.

B. I should let my parents know.

C. I think I can take care of myself.

(  )60. What is the use of the Internet for children?

A. It is used for children to play computer games all day.

B. It is used for children to study or sometimes for fun.

C. It is used for children to chat with friends.

(  )61. What does the passage mainly tell us to do?

A. How to protect (保护)animals. 

B. How to use the Internet.

C. How to be good students

题型:计算题

某汽车发动机的额定功率P=6.0×104W,汽车的质量m=5×103kg,该汽车在水平直路上行驶时所受阻力为车重的0.1倍(g取10m/s2)。求:

(1)汽车在保持额定功率的条件下匀速运动时,速度是多大?

(2)若汽车以8m/s的速度匀速行驶,汽车发动机的功率是多少?

题型:计算题

2011年6月8-9日,中国海军共11艘护卫舰从东海经冲绳本岛与宫古岛间的公海水道驶向太平洋。中国国防部明确表示,这是中国海军的年度计划内例行性训练,符合相关国际法准则,不针对任何特定国家和目标。日本朝野上下对中方的这一举动非常“紧张”,一些右翼更是极力渲染“中国威胁”。日本自卫队统合幕僚长(相当于总参谋长)称:“我们对此高度关注,将根据需要实施警戒监视。”日本《产经新闻》认为,日本政府应联合美国及一些“遇到同样问题”的东南亚国家,一起对中国保持“警戒和监视”。

运用《政治生活》的知识回答:日本对中方的太平洋演习非常“紧张”,主张对中国保持“警戒和监视”的原因是什么?中国应如何应对?

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题型:计算题

检修工应详细询问()掘进机工作情况。

A.当前

B.最后运行时

C.最近

D.上一班

题型:计算题

拍卖师的表达能力主要体现在口齿方面,具体表现为()。

A.语速快

B.表达清晰

C.会多种语言

D.表达准确

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