题干

如图所示,有一质量不计的杆AO,长为R,可绕A自由转动.用绳在O点悬挂一个重为G的物体,另一根绳一端系在O点,另一端系在以O点为圆心的圆弧形墙壁上的C点.当点C由图示位置逐渐向上沿圆弧CB移动过程中(保持OA与地面夹角θ不变),OC绳所受拉力的大小变化情况是(  )

A:逐渐减小

B:逐渐增大

C:先减小后增大

D:先增大后减小

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答案(点此获取答案解析)

C

同类题1

阅读下列文言文语段,完成下列小题。

    【甲】天下事有难易乎?为之,则难者亦易矣;不为,则易者亦难矣。人之为学有难易乎?学之,则难者亦易矣;不学,则易者亦难矣。

    吾资之昏,不逮人也,吾材之庸,不逮人也;旦旦而学之,久而不怠焉,这乎成,而亦不知其昏与庸也。吾资之聪,倍人也,吾材之敏,倍人也;屏弃而不用,其与昏与庸无以异也。圣人之道,卒于鲁也传之。然则昏庸聪敏之用,岂有常哉?

    蜀之鄙有二僧:其一贫,其一富。贫者语于富者曰:“吾欲之南海,何如?”富者曰:“子何特而往?”曰:“一瓶一钵足矣。”富者曰:“吾数年来欲买舟而下,犹未能也,子何恃而往?”越明年,贫者自南海还,以告富者,富者有惭色。

    西蜀之去南海,不知几千里也。僧富者不能至而贫者至焉。人之立志,顾不如蜀鄙之僧哉?是故聪与敏,可恃而不可恃也;自侍其聪与敏而不学者,自败者也。昏与庸,可限而不可限也;不自限其昏与庸,而力学不倦者,自力者也。

(选自《为学》)

    【乙】欧阳公①四岁而孤②,家贫无资。太夫人③以获④画地,教以书字。多诵古人篇章。及其稍长,家无书读。就闻里⑤士人家⑥借而读之,或因而抄录。以至昼夜忘寝食,惟读书是务⑦。自幼所作诗赋文字⑧,下笔已如成人。

(选自《欧阳公事迹》)

【注释】①【欧阳公】指欧阳修。②【孤】幼年丧父。③【太夫人】指欧阳修的母亲。④【获df】多年生草本植物,与芦苇相似。⑤【间里】乡里。⑥【士人家】读书人家。⑦【惟读书是务】即“惟务读书”。务,致力,从事。⑧【文字】文章。

同类题2

阅读理解

    When I was 12, all I wanted was a signet(图章)ring. They were the “in” thing and it seemed every girl except me had one. On my 13th birthday, my Mum gave me a signet ring with my initials(姓名首字母) carved into it. I was in heaven.

    What made it even more special was that it was about the only thing that wasn't being “replaced”. We'd been burnt out in fires that swept through our area earlier that year and had lost everything—so most of the “new” stuff(东 西)we got was rally just to replace what we'd lost. But not my ring. My ring was new.

    Then, only one month later, I lost it. I took if off before bed and it was missing in the morning. I was sad and searched everywhere for it. But it seemed to have disappeared. Eventually, I gave up and stopped looking for it. And two years later, we sold the house and moved away.

    Years passed, and a couple of moves later, I was visiting my parents' when Mum told me that she had something for me. It wasn't my birthday, nor was it Easter or Christmas or any other gift-giving occasion. Mum noticed my questioning look. “ You'll recognize this one.,” she said smiling.

    Then she handed me a small ring box. I took it from her and opened it to find my beautiful signet ring inside. The family who had bought our house 13 years earlier had recently decided to do some redecorations, which included replacing the carpets. When they pulled the carpet up in my old bedroom, they found the ring. As it had my initials carved into it. They realized who owned the ring. They'd had it professionally cleaned up by a jeweler before sending it to my mother. And it still fits me.