题干

如图所示,用食指顶起一把金属勺子保持水平平衡状态,OA段和OB段的重分别为G1和G2.则下列判断正确的是(  )

A:G1>G2

B:G1<G2

C:G1=G2

D:无法判断

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答案(点此获取答案解析)

B

同类题4

阅读理解

    One day. One lifetime. You can do it! From the museum of modern art to the museum of ancient articles, visit our picks for the world's best museums.

National Gallery of Canada (Ottawa)

    This museum has a great collection of art spanning the Middle Ages to the present day, including American, Indian, European, Inuit and Canadian works. It offers a unique, near-complete overview of Canadian art — from early Quebec religious work, through Inuit work from the 1950s, to the contemporaries.

Tokugawa Art Museum (Japan)

    The Tokugawa family reigned over Japan from 1600 to 1868. Under them, the country enjoyed the longest period of peace in its history. This time span is also known as the Edo period, during which the arts flowered in Japan. Artists of this period directly influenced Western masters such as Monet, Gauguin and Whistler and have since gone on to become household names. Other exhibits effectively present, through accurately reproduced environments, aspects of Japanese life at the time.

    Museum of Fine Arts (Boston)

    Highlights of this museum's collection include a 4th-century Christian marble bust (半身像) of St. Paul at prayer, and a painting that questions life and our very existence, Gauguin's “Where do we come from? What are we? Where are we going?” It's a must — go in the US.

The Egyptian Museum (Cairo)

    As well as gathering together some of the finest archaeological finds from all Egypt, this museum also provides a rare opportunity to simply pop in and within minutes be standing face-to-face with one of the greatest works of mankind, Tutankhamun's golden mask. A portrait of unbelievable quality, craftsmanship and beauty, the highly polished gold face — at once a god, a king and a teenager — shines like water: delicate, yet untouchable all at the same time.

同类题5

生石灰是一种传统的建筑材料,俗称“石灰”. 安徽凤阳大量石灰厂在石灰窑中煅烧石灰石制得“石灰”,其反应原理是____ (用化学方程式表示).化学兴趣小组的同学对某石灰厂刚出窑的“石灰”的成分进行探究.

【提出问题】刚出窑的“石灰”有哪些成分?

【猜想】I.只有氧化钙Ⅱ.只有碳酸钙Ⅲ.____.

【查阅资料】碱和碳酸盐同时存在时,酸碱中和反应优先于酸与碳酸盐的反应.

实验探究】

(1)甲同学取一定量的“石灰”样品于试管中,并加入一定量的水,振荡,有白色不溶物.甲同学据此认为试管中的固体为碳酸钙,即猜想II成立.乙同学认为上述实验不足以证明猜想II成立,其理由是____.

(2)乙同学取一定量的“石灰”样品于试管中,加入一定量的水,触摸试管外壁,感觉发热;继续向试管中加入几滴稀盐酸,没有发现气泡产生.乙同学据此认为试管中的固体只有氧化钙,即猜想I成立.丙同学认为乙同学的实验不足以证明猜想I成立,理由是____ .

(3)丙同学认为利用感觉温度变化的方法判断是否有氧化钙不可靠,他用水、酚酞试液和稀盐酸证明了猜想Ⅲ成立,请完成他的实验报告.

实验步骤

实验现象

实验结论

①____ 


②____ 

①____

②____

猜想Ⅲ成立

【思考】使用“石灰”的建筑工地上常有一个大的石灰池,使用“石灰”时,先将生石灰倒入池内水中,一段时间后,再取用其中的石灰浆使用.长期使用的石灰池内壁会逐渐增厚,其主要原因是____  (用化学方程式表示).