题干

如图所示,一轻质细杆两端分别固定着质量为mA和mB的两个小球A和B(可视为质点),将其放在一个直角形光滑槽中,已知轻杆与槽右壁成α角,槽右壁与水平地面成θ角时,两球刚好能平衡,且α≠0,则A、B两小球质量之比为(   )

A:cosαcosθsinαsinθ

B:cosαsinθsinαcosθ

C:sinαsinθcosαcosθ

D:sinαcosθcosαcosθ

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答案(点此获取答案解析)

C

同类题1

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                                                                                                            多能鄙事
                                                                                                                 王开林
        ①在明代头号智者刘伯温名下,居然挂靠着一部常识大典——《多能鄙事》,举凡饮食、器用、方药、农圃、牧养、阴阳、占卜之法无不俱载,是当时家家必备的工具书。
        ②“多能鄙事”源自《论语·子罕》。太宰好奇地问子贡:“你们的先生是圣人吧?为何这样多才多艺?”子贡告诉对方:“天意要玉成我们的先生为圣人,就赐予他一些非凡的能力。”孔子听说此事后,不以为然,他的标准答案才叫靠谱:“我年轻时身份低下,所以会干不少粗活儿。”“吾少也贱,故多能鄙事”,孔子强调自己的能力源自于小时候的底层历练,这种诚实非常可贵。
        ③古代的大智者多半出身贫贱,粗活儿干得好,细活儿才干得成。傅说修筑过城墙,吕望贩卖过笊篱,百里奚养过牛,诸葛亮耕过地。顶级文豪苏东坡也酿过糯米桂花酒,以独家烹饪法做出美味可口的红烧猪肉。干粗活儿,并不是可羞可愧的事情,恰恰是他们生命中一段不可或缺的宝贵经历。这说明,大智者的悟性也须接足地气才行。
         ④要了解魏晋名士的绝版风流,就不可不读《世说新语》。在“简傲”类中,描绘嵇康的笔墨尤其传神:嵇康在大树下与好友向秀打铁,贵公子钟会专程来拜访他,他却视而不见,良久不交一语。钟会遭到冷遇,不免感到尴尬,既然搭讪不成,只好溜之大吉。可钟会刚转身,嵇康就用冷冰冰的语气问道:“何所闻而来?何所见而去?”钟会也很机智,口才一流,原版录音是:“闻所闻而来,见所见而去。”嵇康弹琴时,“手挥五弦,目送飞鸿”,固然超逸非凡,但他打铁时,傲睨左右,旁若无人,精气神十足。鼓炉甚乐,打铁亦欢,嵇康这是在做鄙事?简直是在干绝活儿,人格的魅力如火星般迸射。
        ⑤几年前,有位大学生听完讲座,递来纸笔,请我给他写上一句话,我略微沉吟,给他题写了八个字:“多能鄙事,不拘小节。”他对前四个字心存疑惑,请我讲解一下。我说:“鄙事就是那些粗活儿,并没有任何贬义,比如各种各样的庄稼活儿、修理活儿、木工活儿、家务活儿都算。一个人干些粗活儿,从中有所体悟,同样能够获得真知。”为了佐证我的观点,我还给他讲了一个真实的故事。某年,我陪一位朋友去念楼拜访钟叔河先生,听他谈文论道的时间还不如听他侃当年拖板车和做木工活儿的时间多。他告诉我们,家里的书柜、书桌都是他亲手打造的。意犹未尽,钟先生还要我们用手触摸那些旧家具,“几多平整!几多硬扎!几多牢靠!”,得意之情溢于言表。他一直妥善保存着那套自制的精美绝伦的木工模具,视之为镇宅之宝。听我讲完故事,那位大学生恍然明白,多能鄙事并非不务正业,恰恰是对正业的侧方位滋润。(选自《青年文摘》)

同类题5

根据短文理解,选择正确答案。

    One of Scotland's most active centenarians ( 百岁的人), Lady Morton, drove for nearly 80 years. She loved driving and spent the war years as an ambulance driver for Bangour Hospital. Aged 100 she was still driving around Edinburgh, up to Perthshire and elsewhere — the oldest among all the drivers in Scotland. But she had her first ever accident several days after her 100th birthday — she hit a traffic island (a raised area in the middle of a road where people can wait until it is safe to cross) when she took her new car for a drive in Edinburgh.

    Lady Morton, who celebrated her 100th birthday in July, was given a car as a present. She talked about the accident happened that night. “I wasn't going fast, but I hit a traffic island. I couldn't see it, because it had no light, which I think was unbelievable and unreasonable. But I am all right and luckily my car wasn't badly damaged.

    Although Lady Morton had the accident, she didn't plan to stop driving.“Some people are just born to drive, and I think I am one of them. I've been a good driver since the first time I got in a car, she said. “I am musical, so I listen to sound of the car to know when to change gear (档位).

    Lady Morton bought her first car in 1927. The main change she had noticed since then is the traffic. “It's appalling. However, I don't mind it, because I am experienced, but I feel very sorry for beginners,” she said.