问题 单项选择题

火车转弯的地方,钢轨的内外轨是()

A.内轨高

B.外轨高

C.一样高

D.不可确定

答案

参考答案:B

解析:在平直轨道上匀速行驶的火车,所受的合力等于零.在火车转弯时,是什么力作为向心力的呢?原来,火车的车轮上有突出的轮缘,如果转弯处内外轨一样高,外侧车轮的轮缘挤压外轨,使外轨发生弹性形变,外轨对轮缘的弹力就是使火车转弯的向心力.火车质量很大,靠这种办法得到向心力,轮缘与外轨间的相互作用力要很大,铁轨容易受到损坏.如果在转弯处使外轨略高于内轨,火车驶过转弯处时,铁轨对火车的支持力FN的方向不再是竖直的,而是斜向弯道的内侧,它与重力G的合力指向圆心,成为使火车转弯的力.这就减轻了轮缘与外轨的挤压.

阅读理解

Can plants eat people? Probably not, but there are many plants that eat meat. Some of them are big. And they can eat small animals. One famous meat-eating plant is the Venus flytrap(捕蝇草).

The Venus flytrap is a very strange plant. It grows in dry parts of the United States. Its leaves are like the pages of a book. They can open and close very quickly. Inside the leaves, there are three small hairs. If a fly touches one of the hairs, the leaf closes quickly. The fly cannot get out. In about half an hour, the leaf presses the fly until it is dead. Then, the plant covers the fly. Slowly, the plant eats the fly.

Why do plants do it? Most plants get what they need from the sun, the air, and the ground. In some places, the ground is very poor. It doesn’t have all these important things, especially nitrogen(氮).Animal meat has a lot of nitrogen, so some plants eat meat to get what they need. Let’s hope that some of the bigger plants don’t get the same idea!

小题1:The Venus flytrap is a kind of       .

A.plant

B.animal

C.food

D.meat小题2:The Venus flytrap grows in        .

A.most parts of the world

B.some parts of Africa

C.dry parts of the United States

D.wet parts of England小题3:From the passage, we learn that        .

A.all plants can eat people

B.all plants can eat animals

C.some plants can eat people

D.some plants can eat animals小题4:he underlined word “presses” probably means       in Chinese.

A.挤压

B.关上

C.打开

D.松开小题5:Some plants eat animal meat because __________.

A.plants are dangerous to animals

B.animals are dangerous to plants

C.plants want to get what they need from animal meat

D.plants want to protect themselves against animals

论述题

材料一 以色列人达尼埃尔·谢赫特曼因对“准晶体”的研究,而获得2011年度诺贝尔化学奖。传统理论认为,固体物质要么是晶体,要么是非晶体。谢赫特曼的发现开辟了第三种可能,即“准晶体”的发现。

1982年4月,谢赫特曼在一座实验室内研究铝锰合金时,发现一种特殊的“晶体”。他借助电子显微镜获得一幅电子衍射图,发现它具有5次对称性,显现长程有序性。而依据那个时期的理论,晶体不可能具有5次对称性,而非晶体则没有长程有序性。于是,他坚持认为除晶体、非晶体外还有第三种可能。

材料二 获得诺奖的背后,却是谢赫特曼在嘲笑中的坚持。正如他本人回忆说,“我告诉所有愿意听的人,我发现了一种具有5次对称性的材料,但人们只是嘲笑我,”他说,“实验室主管来到我面前,把一本书放在桌上。他说,‘丹尼,你为什么不读读这个?你所说的是不可能的’。当时,著名的化学家、两届诺奖得主鲍林公开说,“达尼埃尔·谢赫特曼是在胡言乱语,没有什么准晶体,只有‘准科学家’” 。今天,勇敢质疑“常识”的谢赫特曼终于获得全世界最权威的科学认可。

材料三 1987年,法国和日本科学家制出足够大的准晶体,可以经由X射线和电子显微镜直接观察。至此,谢赫特曼的理论终于得到科学界的认可。 作为热和电的不良导体,准晶体可用于制作温差电材料,可把热能转换为电能;利用其表面不粘的特性,它可以用于制作煎锅表面涂层。另外,准晶体的潜在应用领域包括制作节能发光二极管和发动机绝热材料。

上述材料如何体现辩证否定观的。(9分)