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图是某课外科技小组的同学设计的厕所自动冲水装置的示意图,它在自来水管持续供给的较小量的水储备到一定量后,自动开启放水阀门,冲洗厕所.实心圆柱体浮体A的质量为5.6kg,高为0.18m,阀门B的面积为7.5×103m2;连接A、B的是体积和质量都不计的硬杆,长为0.16m.当浮体A露出水面的高度只有0.02m时,阀门B恰好被打开,水箱中的水通过排水管开始排出.已知水的密度为1×103kg/m3,不计阀门B的质量和厚度.当水箱开始排水时,求:



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阅读下列短文,从每题所给的四个选项(A、B、C和D)中,选出最佳选项。

      

       I just hope that our brains won’t crash(死机). Are you wo rking on your typing skills to make you a more efficient worker? That may be all for nothing as Intel believes that we’ll be able to control our computers with our brains by 2020.

       Intel and its resear ch partners are study ing how brain acts when it thinks. For example, scientists have found that people’s brains react in a similar manner when asked to think of a bear.

       Through sensors(感应器)that can find this sort of brain activity, Intel thinks that it will be able to read and translate this into an input system thanks to a c hip in the brain.

        “We’re trying to prove you can do interesting things with brain wav es. ”Intel research scientist Dean Pomerleau told Computerworld. “Eventually people may be willing to be, more devoted to brain implants(植入物). Imagine being able to surf the Web with the Power of your thoughts. ”

       Even if thin king about a bear isn’t enough to show that you want to copy and paste something. Intel still thinks that there’s a future in using your brain instead of the keyboard.

        “If we can get to the point where you can accurately find specific words, you could mentally type, ”he added. “You could compose characters or words by thinking about letters flashing on the screen or typing whole words rather than their individual characters. ”

       While this may all sound impractical for present time, Intel thinks that it’s possible and something we’ll all want.

        “I think human beings are unusually adaptive(适应的), ”said Andrew Chien, vice pre sident of research and director of future technologies research at Intel Labs. “If you told people 20 years ago that they would be carrying computers all the time, they would have said, ‘I don’t want that. I don’t need that. ’Now you can’t get them to stop carrying device s. There are a lot of things that have to be done first but I think implanting chips into human brains is well within the scope of possibility. ”

       Make good use of your favorite mouse and keyboard set-up before they’re old-fashioned.