题干

如图示,轻绳两端分别系在圆环A和小球B上,圆环A套在粗糙的水平直杆PQ上.现用水平力F拉着绳上一点O,使小球B从图中的实线位置缓慢上升到虚线位置,但圆环A始终保持在原位置不动,则在这一过程中,环对杆的摩擦力f和环对杆的压力N的变化情况是(  )

A:N不变

B:f增大

C:N减小

D:f不变

上一题 下一题 0.0难度 选择题 更新时间:2019-11-04 03:41:27

答案(点此获取答案解析)

A,B

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    With the Chinese language growing in popularity,the UK government plans to invest(投资)10 million pounds to help more kids learn Mandarin(普通话).Do you think it is necessary for the UK pupils to learn Mandarin?Some people share their opinions online.

    Ted(UK): The learning of any language can be valuable and rewarding,but it is not suitable for everyone. Chinese is a difficult language to learn and the UK has a poor reputation for teaching foreign languages.Why should they learn Chinese when most people in the world speak English?

    Mark(US): I studied French for 2 years in high school and German for 4 years in college.I studied Mandarin informally for about 4 months before moving to China.Now I speak Mandarin every day as my wife doesn't speak English.But it is far from being fluent.Learning additional languages is a great thing,which offers a different perspective on the world around us.Nowadays,it's almost necessary to be able to speak more than just your native tongue.

    George(UK): No,unless they're taught from a very early stage of childhood.Mandarin is so difficult.If China really is going to dominate the world,it'll have to do so by speaking the world's dominant language—English.

    Sam(UK): I don't think Chinese will become as widely spoken throughout the world as English.It is too difficult to learn as a second language.To learn Chinese you completely have to devote yourself to learning how to write and read it.If you have to learn it besides other subjects you can't be good at it.But Chinese will become more popular, and that is a good thing.