题干

如图,护城河上的吊桥装置是巧妙应用杠杆的例子,请在图中画出动力F1、阻力F2和动力臂l1

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答案(点此获取答案解析)

解:(1)B点为支点,动力F1沿AC方向,过支点B作垂直于动力作用线的垂线段(即动力臂L1).

(2)阻力作用点为AB的中点,然后过作用点作竖直向下的力(即阻力F2);如图所示:

同类题3

阅读下面四篇短文,从每题所给的A、B、C、D四个选项中选出最佳选项。

    If you are walking through Newyork's Central Park on a fine summer day, you might come across a group of children listening to a story. The storyteller will be sitting beside a statue of a kindly looking man holding an open book. Although this man never actually visited New York, his fame as a writer of fairy tales and children's stories has spread far beyond his homeland.

    Hans Christian Andersen is recognized as a key figure in 19th-century romantic fiction. He is, without question, the best-known writer Denmark has ever produeed. His stories continue to delight children and adults the world over. Classic tales such as The Little Mermaid, The Ugly Duckling, and The emperor's New Clothes are loved for their humor and imagination. They are loved for the simple but meaningful messages they often contain.

    Born on April 2, 1805, in Odense, Demark, Andersen was an imaginative child. His father, a poor shoemaker, died in 1816. With a mother who was unable to read or write, the boy received little education as a child. At 14, Andersen traveled to Copenhagen. He was lucky enough to spend some time with the Royal Theater, but when his voice changed, he had to leave. Luckily, one of the directors helped him by arranging his education.

    Andersen went to the University of Copenhagen in 1828, and his literary career began soon afterwards. He hoped to achieve success with poems and plays, and made too low an estimate(估计) of the kind of stories which have made him famous. Though not particularly fond of children, he had a gift for entertaining them. This led a friend to suggest he write down the stories he invented.

    Many of Andersen' s tales are based on folklore(民间故事), and many are products of his own imagination. All of them are told in a humorous and informal style that children loved from the start.

    Before his death in 1875, Andersen regularly traveled around Europe, and was warmly welcomed everywhere he went.

    Nowadays, of course, Hans Christian Andersen is a household name. Whether he would have liked or not, millions of children and adults will always be grateful for the magie his stories have brought to their lives. The young listeners in Central Park are proof of that.