[题目]宽9 m的成型玻璃以2 m/s的速度连续不断地向前行进.在切割工序处.金刚割刀的速度为10 m/s.为了使割下的玻璃板都成规定尺寸的矩形.则:(1)金刚割刀的轨道应如何控制?(2)切割一次的时间多长?(3)所生产的玻璃板的规格是怎样的? 题目和参考答案——青夏教育精英家教网—

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【题目】宽9 m的成型玻璃以2 m/s的速度连续不断地向前行进，在切割工序处，金刚割刀的速度为10 m/s，为了使割下的玻璃板都成规定尺寸的矩形，则：

（1）金刚割刀的轨道应如何控制？

（2）切割一次的时间多长？

（3）所生产的玻璃板的规格是怎样的？

【答案】（1）割刀速度方向与玻璃板速度方向成arccos角度（2）0．92 s （3）长9 m、宽1．84 m

【解析】（1）由题目条件知，割刀运动的速度是实际的速度，所以为合速度．其分速度的效果恰好相对玻璃垂直切割．

设割刀的速度v1的方向与玻璃板速度v2的方向之间的夹角为θ，如图所示。要保证割下均是矩形的玻璃板，则由v1是合速度得v2＝v1cos θ

所以cos θ＝＝，即θ＝arccos

所以，要割下矩形板，割刀速度方向与玻璃板速度方向所成角度为θ＝arccos

（2）切割一次的时间t＝＝ s≈0．92 s

（3）切割出的矩形玻璃板的规格为：长度d＝9 m

宽度：l＝v2t＝2×0．92 m＝1．84 m

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【题目】B

Katharine Graham, once described as ＂the most powerful woman in America＂, was the owner and publisher of The Washington Post newspaper. Under her leadership, it became one of the most important newspapers in the country.

Katharine Graham was born in New York in 1917. Graduating from the University of Chicago in 1938, Katherine got a job as a reporter for a newspaper in San Francisco, California. In 1933, Katharine’s father bought a failing newspaper, The Washington Post. It was the least successful of five newspapers in Washington.

Soon Katharine returned to Washington and got a job editing letters to the editor of her father’s newspaper. In 1946, her husband Philip Graham became publisher of The Washington Post. When she was 46, her husband died, leaving Katharine Graham four children to raise and a newspaper to operate.

At first, she was concerned only with finding a way to keep control of The Washington Post until her sons were old enough to lead it. She had no training in business or experience in operating a large company and decided to learn. She hired excellent reporters and editors. In 1969, Missus Graham became publisher as well as president of The Washington Post company. In the 1970s, The Washington Post became famous around the world. Katharine Graham also played an important role in supporting women by employing more of them. When she was eighty years old, Katharine Graham wrote a very popular book called Personal History about her life, which won a Pulitzer prize for biography in 1998. Friends of Katharine Graham said she used her intelligence and bravery to improve the American media.