问题 应用设计题

在自动化生产线上,常用传送带传送工件,如图所示,一个工件与传送带一起沿水平向右做加速运动,不计空气阻力,请在图中画出工件受到的所有力的示意图.

答案

物体受到重力和支持力作用,由于物体沿水平向右做加速运动,物体相对于传送带有向左的运动趋势,所以物体受到向右的摩擦力,所以物体共受三个力作用:重力、支持力和摩擦力;

重力方向竖直向下,作用点在重心,支持力方向竖直向上,作用点也画在重心上,摩擦力方向水平向右,作用点也画在重心上

阅读理解

Johann Gutenberg, who worked as a goldsmith(金匠),took what has already been discovered, and created a small invention that changed history. He created a machine that allowed him to move small blocks of letters in such a way that written material could be printed and mass-produced. Few people could read before Johann Gutenberg made the invention, but once books became less expensive, more Europeans could read and write.

Block printing existed long before Gutenberg. The Chinese had been using wood blocks to print books as early as 868, but a new set of woodcuts(木刻印版) had to be made for each book. Producing one book was not easy; producing all kinds of books was more difficult.

Writing ink dates from about 2500 BC in Egypt and China. Johann Gutenberg use an oil-base printing ink that would last longer than other inks used in his time. We don’t know much about Gutenberg because he was not famous during his lifetime. He was born in Germany about 1400. In 1448, Gutenberg developed signatures for each number, letter, and punctuation mark(标点符号). He then built the molds (模型) to hold the signatures in place. Johann Gutenberg published the first mass-produced book: a 1,282 page Bible. To this day, more copies of the Bible have been printed the any other book.

Copies of Gutenberg’s invention spread throughout Europe, but the German goldsmith did not get rich from his invention. Some officials denounced the invention of printing because they feared that it would spread bad ideas. By 1500 there 1,700 printing presses in Europe. The presses had already produced about 20 million volumes of 40,000 different books.

小题1:What happened after Johann Gutenberg’s invention?

A.People could afford to read books.

B.People became interested in inventing.

C.It was still difficult to print all kinds of books.

D.Punctuation mark began to be used in printing.小题2:Compared with block printing in China, Johann Gutenberg’s method __________.

A.was difficult to run.

B.needed harder paper

C.used a new kind of ink

D.was put into use earlier小题3:The underlined word “denounced” in the paragraph means __________.

A.fought against

B.accepted

C.laughed at

D.supported小题4:What is the best title for the passage?

A.A famous 1,282 page Bible

B.The life of a famous inventor

C.An invention that changed history

D.The development of printing

问答题 论述题