题干

小明同学在学习了课本上的关于《测定家用电冰箱每天消耗的电功》的实验后,实际测量了他家的电冰箱的耗电量.他按照要求,提前做好了准备工作,用时钟测出了冰箱在20min内持续工作了6min,从而求出了冰箱的“工作时间系数”(在某段时间内电冰箱的实际工作时间与这段时间的比值)η= ____,那么这台电冰箱每天(24h)的工作时间t= ____ h,最后根据电冰箱铭牌上的所表明的额定电功率P=150W,计算出此电冰箱每天消耗的电功W= ____ KW·h.

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答案(点此获取答案解析)

30%,7.2,1.08

同类题4

阅读下面的短文,然后根据短文内容,在每小题所给的四个选项中选出最佳选项。
                                                                                          C
  “How are you?” is a nice question. It's a friendly way that people in the USA greet each other. But “How are you” is also a very unusual question. It's a question that often doesn't need an answer. The person who asks “How are you?” hopes to hear the answer “ Fine”, even if the person's friend isn't fine. The reason is that “How are you?” isn't really a question and “Fine” isn't really an answer. They are simply other ways of saying “Hello” or “Hi”.
    Sometimes, people also don't say exactly what they mean. For example, when someone asks “Do you agree?” the other person might think, “No, I disagree. I think you’re wrong…” But it isn't very polite to disagree so strongly, so the other person might say “I'm not sure.” It's a nicer way to say that you don't agree with someone.
    People also don't say exactly what they are thinking when they finish talking with other people. For example, may talks over the phone finish when one person says “I've to go now.” Often, the person who wants to hang up gives an excuse “Someone's at the door.” “Something is burning on the stove.” The excuses might be real, or not. Perhaps the person who wants to hang up simple doesn't want to talk any more, but it isn't polite to say that. The excuse is more polite, and it doesn't hurt the other person.
    Whether they are greeting each other, talking about an idea, or finishing a talk, people don't say exactly that they are thinking. It's an important way that people try to be nice to each other, and it's part of the rule of the game of language.