题干

关于做功和功率的说法中正确的是(   )

A:功率大的做功一定多

B:物体做功越多,功率越大

C:由静止自由下落的物体,重力做功功率变大

D:在光滑水平面上做匀速直线运动的物体,支持力不做功,功率为零

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答案(点此获取答案解析)

C,D

同类题1

阅读下面短文,回答问题。

      第二要乐业。“做工好苦呀!”这种叹气的声音,无论何人都会常在口边流露出来。但是我要问他:“做工苦,难道不做工就不苦吗?”今日大热天气,我在这里喊破喉咙来讲,诸君扯直耳朵来听,有些人看着我们好苦;翻过来,倘若我们去赌钱去吃酒,还不是一样在淘神费力?难道又不苦?须知苦乐全在主观的心,不在客观的事。人生从出胎的那一秒钟起到咽气的那一秒钟止,除了睡觉以外,总不能把四肢、五官都搁起不用。只要一用,不是淘神,便是费力,劳苦总是免不掉的。会打算盘的人,只有从劳苦中找出快乐来。我想天下第一等苦人,莫过于无业游民,终日闲游浪荡,不知把自己的身子和心子摆在哪里才好。他们的日子真难过。第二等苦人,便是厌恶自己本业的人,这件事分明不能不做,却满肚子不愿意做。不愿做逃得了吗?到底不能。结果还是皱着眉头,哭丧着脸去做。这不是专门自己替自己开玩笑吗?我老实告诉你一句话:“凡职业都是有趣味的,只要你肯继续做下去,趣味自然会发生。”为什么呢?第一,因为凡一件职业,总有许多层累、曲折,倘能深入其中,看他变化、进展的状态,最为亲切有味。第二,因为每一职业之成就,离不了奋斗;一步一步的奋斗前去,从刻苦中将快乐的分量加增。第三,职业性质,常常要和同业的人比较骈进,好像赛球一般,因竞胜而得快乐。第四,专心做一职业时,把许多游思、妄想杜绝了,省却无限闲烦恼。孔子说:“知之者不如好之者,好之者不如乐之者。”人生能从自己的职业中领略出趣味,生活才有价值。孔子自述生平,说道:“其为人也,发愤忘食,乐以忘忧,不知老之将至云尔。”这种生活,真算得人类理想的生活了。

同类题3

阅读理解

    A small group of people around the world have started implanting(移植) microchips to link the body and the computer.

    Mr. Donelson and three friends, who had driven 100 miles from their homes in Loockport, New York, to have the implants put in by Dr. Jesse Villemaire, whom they had persuaded to do the work, are part of a small group, about 30 people around the world, who have independently put in microchips into their bodies, according to Web-based reports.

    At a shop William Donelson was having a four-millimeter-wide needle put into his left hand. “I'm set,”he said with a deep breath. He watched as the needle pierced(刺穿) the fleshy webbing between his thumb and a microchip was set under his skin. At last he would be able to do what he had long imagined: strengthen his body's powers through technology.

    By putting the chip inside—a radio frequency identification device (RFID)—Mr. Donelson would have at his fingertips the same magic that makes safety gates open with a knock of a card, and bridge and tunnel traffic flow smoothly with an E-Zpass. With a wave of his hand he plans to connect with his computer, open doors and unlock his car.

    Implanting the chip was relatively simple task but very meaningful to Mr. Doneselson, a 21-year-old computer networking student so interested in the link between technology and the body that he has data-input jacks(数据输入插空) inside his body. They might lead to an imagined future when people can be connected directly into computers. His new chip is enclosed in a glass container no bigger than a piece of rice and has a small memory where he has stored the words “Technology”.

    Some doctors have done the piercing in people's homes, and others have implanted chips in their offices after patients signed forms showing the fact that long-term studies have not been done on their safety. Piercers treat the implants much like any other medical operation steps, instructing people to keep the site dry, and advising them that swelling and redness should last a week.

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