题干

如图,MNP为竖直面内一固定轨道,其圆弧段MN与水平段NP相切于N、P端固定一竖直挡板.M相对于N的高度为h,NP长度为s.一木块自M端从静止开始沿轨道下滑,与挡板发生一次完全弹性碰撞后停止在水平轨道上某处.若在MN段的摩擦可忽略不计,物块与NP段轨道间的滑动摩擦因数为μ,求物块停止的地方与N点距离的可能值.


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答案(点此获取答案解析)

根据功能原理,在物块从开始下滑到停止在水平轨道上的过程中,物块的重力势能的减少△EP与物块克服摩擦力所做功的数值相等.△EP=W

设物块的质量为m,在水平轨道上滑行的总路程为s′,则△EP=mgh,W=μmgs′

连立化简得s′={#mat

同类题4

先通读下面的短文,然后根据短文内容,在文章后表格的空格内填入一个最恰当的单词。每个空格只能填一个单词。

    Yu Minhong, president of New Oriental Education, shared his ideas with the young after the English speech competition of the 14th China Daily. Here is some of his advice to young people:

    “One suggestion I'd like to give you is that it's important to do what you like without fear of failure. And the process(过程)of working toward your dreams matters more than the results. Young people should take chances to show off talents. Take competitions like this one as an example: If you are afraid to fail, you'll never get the chance to stand on the stage and make a speech. Above all, it's most important to take part.

    Another suggestion I want to give you is to read books. It is not easy to keep reading every day. For me, it is much more difficult and challenging to keep reading and taking notes every day than it is to walk 10,000 steps.”

    In his speech, Yu also shared his view on life. He chose a different life rather than a more successful one. He uses the famous lines of American poet Robert Frost (1874–1963) to make his point:“Two roads diverged (分叉) in a wood, and I … took the one less traveled by, and that has made all the difference.”Yu pointed out, “Your happiness should not be what others think you should run after, but instead you should decide what it is. It is you who should make choices for your own life.”

    Yu Minhong's speech to young people

His advice

● He thinks the process is more ____ than results,so young people should take chances to show off their ____.

● He also suggests that we should read books. It's ____ to keep reading all the time.

His views on life

● Yu prefers a different life ____ a more successful one.

● He says that your happiness should be decided by ____instead of what others think.