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Площадь большого поршня гидравлического пресса 375 мс^2.Какой должна быть площадь малого поршня, чтобы поднять груз весом 12кН,применяя силу 160 Н
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Fгруза/Sбольшого поршня = Fчеловека/Sмалого поршняSмалого поршня = Fчеловека*Sбольшого поршня/Fгруза = 160*375/12000= 5 см^2 должна быть площадь малого поршня.
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Автор:
pintoulxx - 6 лет назад
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Упражнение 12. Укажите, какие из следующих утверждений соответствуют содержанию текста 4А
6. Only a few years ago colour television was rapidly replacing black-and-white television. 7. When the war was over, TV sets stopped coming off factory assembly lines. 8. After World War II TV sets began coming off factory assembly lines.
Television
The television set is evidently the most important and popular electronic product of all time. All homes in developed countries have one or more TV sets and in many countries there are considerably more TV sets than telephones.
But in 1939 at the World's Fair in New York a tiny nine-by-twelve inch box was the centre of attention for hundreds of people. They were the first to see a television set in action. Compared to today's TV shows of underwater and outer-space research, those first black-white pictures were not very good. The pictures were only transmitted from one side of the Fair territory to the other. But in 1939 they were of historical importance.
Within a few days the news of television spread throughout the world. A lot of people wanted to have a look at the new invention. Everyone was interested in it. But only few people owned television sets in the next few years. When World War II broke out2 electronic factories that began the TV production stopped making them and started making war materials instead. When the war was over, TV sets began coming off factory assembly lines. By 1958 there were millions of them.
In a surprisingly short time people watched fewer films and turned from newspapers and magazines to TV. In its short history television has had great influence on people's life and way of thinking. Rocket-launching, concerts and football and tennis matches can be seen direct as they occur. The boundaries of time and space have disappeared.
At present TV communication is provided with the help of a system of artificial earth satellites so that people living in different parts of the country and all over the world and in different time zones are able to watch the central TV programs at the most convenient hours.
Nowadays many countries also have cable TV, a system using wires for the transmission of television programs (like telephone calls). Cable television first appeared in 1949 as a means of transmitting TV signals to rural and mountain areas far from big cities. Cable television's next big step forward was made by the mid — 1980s. Scientists announced that many technical problems had been solved and in the future it would be possible via satellite and cable TV to use more channels on a TV set at every home in the world.
Then we saw how a new technical invention, colour television, was rapidly replacing black-and-white television. Recently it was reported that the first pocket-size3 colour television set had been developed. It was stated that a liquid-crystal display4 was used similar to those on calculators and watches and that it weighed less than a pound.
A few years ago it became evident that the next major advance for TV would be digital television. In a digital system the usual continuous signal is replaced by a digital code containing detailed information on brightness, colour, etc. A digital TV set hangs on the wall like a picture. Essentially, it is a minicomputer with a visual display. Once a week5 you put the programs you like into the memory, and the TV set will automatically switch on the desired channel at the right time. You can watch several programs simultaneously on miniscreens and then produce one of them in full format. Also, the TV set can automatically video-record the programs when you are absent or occupied.
By the end of 1980s television has moved to a new and the most important stage in its development since the appearance of colour television. Technically it is called high-definition television (HDTV)6 or Hi-Vision. This is the much higher resolution television7 of the 21st century. This revolution was started by Japanese manufacturers when they developed a new video system with a picture resembling a wide-screen film more than traditional television. The new system increases the screen's width-to-height ratio8 (16:9). The result is a picture several times sharper than in the existing TV sets. Besides, recent developments in plasma display panel technology9 make HDTV commercially practicable. The plasma display makes it possible to produce a large, bright, colour, flat TV screen so thin and light that it can also be hung on a wall like a framed picture. The engineering problem that has existed almost since the first days of television may be solved now.-
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