题干

如图所示,倾角为30°的光滑斜面上有一个质量为1kg的物块,受到一个与斜面平行的大小为5N的外力F作用,从A点由静止开始下滑30cm后,在B点与放置在斜面底部的轻弹簧接触时立刻撤去外力F,物块压缩弹簧最短至C点,然后原路返回,已知BC间的距离为20cm,取g=10m/s2,下列说法中不正确的是(   )

A:物块经弹簧反弹后恰好可以回到A点

B:物块从A点到C点的运动过程中,克服弹簧的弹力做功为4J

C:物块从A点到C点的运动过程中,能达到的最大动能为3J

D:物块从A点到C点的运动过程中,物块与弹簧构成的系统机械能守恒

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答案(点此获取答案解析)

A,C,D

同类题4

阅读理解

B

    These days, young people in some English-speaking countries are speaking a strange language, especially when communicating on social media.

    Look at these words chosen by The Washington Post: “David Bowie dying is totes tradge,” and “When Cookie hugged Jamal it made me totes emosh.” Or this sentence: “BAE, let me know if you stay in tonight.”

    What on earth do they mean? Well, “totes” is a short form of “totally”. Similarly, “tradge” means “tragic” and “emosh” means “emotional”. It seems that, for millennials(千禧一代), typing in this form is not only time-saving but fashionable.

    As you can see, many millennial slangs(俚语)are formed by so-called “totesing”—the systematic abbreviation(缩写)of words. The trend might have started with “totally” becoming “totes”, but it now has spread to many other English words.

    The origins of other millennial slangs are more complex than “totesing”.“Bae”, for example, has been widely used by African-Americans for years. It can be an expression of closeness with one's romantic partner or, like “sweetheart”, for someone without romantic connection. After pop singer Pharrell used the word in his work, “bae” became mainstream.

    Some people might think millennial slangs lower the value of the English language, but Melbourne University linguist(语言学家)Rosey Billington doesn't agree. She says when people are able to use a language in a creative way, they show that they know the language rules well enough to use words differently. Two other linguists, Lauren Spradlin and Taylor Jones, share the same view. The two analysed hundreds of examples of totes-speak and discovered totesing has complex roots.

    It isn't simply an adult version of baby talk, nor a clever way to minimize your word count. Rather, it is a highly organized system that relies on a speaker's mastery of English pronunciation. It is about sounds, follows sound system of English and has strict rules.