Предмет: Математика, автор: atroshkind

Дюралюминий-сплав, состоящий из 83 частей алюминия, 5 частей меди, 1 части марганца и 1 части магния (по массе). Какова масса куска дюралюминия, если в нем меди больше, чем магния, на 84г.

Ответы

Автор ответа: CVita

0

найдем разницу в частях между медью и магнием
5-1=4
найдем массу в граммах одной части
84:4=21 гр
найдем общее количество частей
83+5+1+1=90
найдем массу сплава
21*90=1890 гр

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THE NANOBOTS!
Scientists recently created a microscopic robot that can crawl along molecules of DNA. Combining the science of molecular biology and nanotechnology, this unique mechanism, dubbed a 'nano-spider', was developed by a team of researchers from Columbia University in New York with the help of colleagues in Arizona, California and Michigan. The groundbreaking device measures a mere four nanometres in width-an amazing 100.000 times smaller than the diameter of a10 human hair.
Needless to say, this nano-spider is no WALL-E, but it can still be classified as a robot. A robot is defined as a mechanism that can understand its surrounding environment, make decisions and move automatically. The little spider-bots can certainly do that. They can walk, turn left and right and even create their own products. One day, such microscopic devices could actually be used to build tiny computer chips or to detect and treat diseases such as cancer at a molecular level.
It is interesting to note that the nano-spiders are made of DNA molecules. The spider's body is composed of a common protein called streptavidin. Unlike a real spider, however, the nano-spider has only got four legs which are single strands of DNA protein attached to the body.
Microscopic DNA walkers have been developed in the past, but they have never managed more than three steps. These ones can manage as many as 50 steps, which means a possible walking distance of around 100 nanometres. Taking up to one hour to complete, this is more like a marathon for the nano-spider. However, researchers hope to be able to make the spiders walk faster and further in the future. Furthermore, present research is focusing on making the nano-spiders able to follow more commands and to make more decisions.
Molecular robotics is a new field in scientific research. Although it has not produced a long list of great inventions yet, scientists believe that nanotechnology could become one of the most important industries in the near future. The nano-spider is considered to be an important step in research which could one day lead to devices being created for various medical applications. One day, people could live their lives with miniature robot surgeons patrolling and protecting the insides of their bodies. For example, the spiders could be programmed to check a cell in the body, decide if it is cancerous, and then administer an anti-cancer drug.
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1)In the first paragraph, the writer says that the nano-spider

A is much thicker than a human hair.

B cannot be seen under a microscope.

C was invented by an individual scientist.

D is an extremely small machine.

2. Why does the writer suggest nano-spiders can be classified as robots?

A because they have the features of a robot

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D because they are microscopic devices

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B the walking distance a DNA walker can do

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D the time each step takes for a DNA walker

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B They are already being used to fight cancer.

C They have been used for various medical purposes in the past.

D They have not actually been invented yet.

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C There are concerns about whether the industry has strict rules for safety.

D There are no concerns about nanotechnology in medicine.

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