[Archive!] Pure mathematics, physics, chemistry, etc.: brain-training problems not related to trade in any way - page 34
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Да, средняя плотность воздуха уменьшится и вес упадёт. Но, только тонну мух я себе с трудом представляю в самолёте.
let's remember Yuri:
So you think that if I get into this plane with a strong fan and turn it on, the pressure on all the walls will increase, and equally so ? It's a treasure trove, you could make a perpetual motion machine. Then you wouldn't need a forecaster. And mankind would benefit. A lot. :-)
... no comment.
and once we close the door, the weight will increase by a ton. Colleagues, you have invented the perpetual motion machine!!! Congratulations. All you have to do is find someone to slam the door... and feed the flies.
There' s an articlehere about an aeroplane task. A couple of quotes:
Распространение задачи по Интернет-форумам происходило с катастрофической скоростью, превращая даже самые спокойные и тихие форумы — в арену флейма. За это свойство задачка получила название «ментального вируса».
And Swetten must have known about it, but now she's sleeping peacefully...
Unfortunately, we too have not escaped the sad fate. There's still a fierce shambles going on in the discussion. Anonimus, before you vent your righteous anger here and explain to everyone what will actually happen to the plane, think about the following: The best minds in the world can't solve this problem. How could you, with your incomplete high school education?
There' s a taskhere about an aeroplane. A couple of quotes:
And Swetten must have known about it, but now she's sleeping peacefully...
What'd I tell you? It's all her fault. She pushed the men and went to bed herself.
A ton of flies hovering in the air expends their energy heating the air. The pressure of the air that is being heated increases. The mass of the whole box remains constant, hence its weight. If we open the door, the pressure is equal to the atmospheric pressure by letting the air out of the box, hence its total mass, and hence its weight, is reduced.
When we close the door again, the weight will be the same as at the beginning of the experiment minus the lost mass of the flies, because they have already lost weight. :)))
A ton of flies hovering in the air expends their energy heating the air. The pressure of the air that is heated increases. The mass of the whole box remains constant and so does its weight. If we open the door, the pressure is equal to the atmospheric pressure by letting the air out of the box, so the total mass of the box is reduced, and therefore its weight is also reduced.
What I meant was that the flies will fly out when the door is opened. The average air density decreases. The aircraft is left with clean air, which has a lower average density. For example, the average air density with flies is 1300 gm3, without flies is 1200 gm3.
Я имел ввиду то, что при открывании двери мухи вылетят. Средняя плотность воздуха уменьшается. В самолёте остаётся чистый воздух, средняя плотность которого меньше. Например, ср.плотность воздуха с мухами - 1300 кг\куб.м, без мух - 1200 кг\куб.м.
Why mention air density if the flies fly away? Then of course the system will lose mass, and if you take the plane out, it'll make the box even lighter. :)
Here is the solution of the problem about a plane with a transporter.
Движение самой взлётной полосы при решении задачи несущественно, поскольку при этом не возникает силы в горизонтальной плоскости, сопоставимой по порядку величины с силой тяги авиационного двигателя. Рассмотрим, в качестве примера, случай, когда полотно движется навстречу самолету со скоростью равной по модулю скорости движения самолёта относительно земли. Это не остановит самолёт относительно наблюдателя, стоящего на земле (как это произошло бы с едущим автомобилем или с бегущим по полотну человеком), - просто колёса самолёта будут вращаться вдвое быстрее, чем при неподвижном полотне. Аналогично можно показать, что любое движение взлетной полосы приводит лишь к изменению скорости вращения колес самолета, но не влияет на движение самого самолета. Транспортером можно остановить вращение колес, но не сам самолет. Другими словами - не существует такой скорости движения полотна, чтобы самолет остановился относительно земли .
Unobvious... although the same argument vaguely arose in my mind at the start of the discussion, but I hesitated to express it. And one more fact:
1. The words "spinning the wheels of an aeroplane" were added to the condition by the Russians.
It is interesting that in the original English problem there is no word about "rotation of wheels" ( A plane is standing on runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction). The question is: Will the plane take off or not? Will it be able to run up and take off?) However, even in such a quite physically correct variant of the problem caused a lot of discussions.
This kind of "mutation" towards further complication is quite typical for media viruses.
An aircraft (jet or propeller) stands on a runway with a movable surface (like a transporter). The runway can move against the direction of take-off of the aircraft. It has a control system that monitors and adjusts the speed of the runway so that the speed of the aircraft's wheels is equal to the speed of the runway. Question: can the plane take off under these conditions?
Everything will depend on the ratio of engine thrust to friction force of the wheels, the more powerful engines vs. friction force, the less time the wheels will be overloaded and consequently can keep their function until they will fly off the surface, otherwise the wings will lie on the runway, and born to crawl as you know can not fly :)
The problem should be reversed and solved vice versa, the aircraft is landing on the runway which is moving in the direction of its movement :)
Here is the solution.
I agree with the one quoted above. It will take off. But if there were no jet engine and propeller, and the plane was accelerated by wheels, it would not take off.
Mathemat, I want to repeat that the pressure at the bottom of the barrel is higher than the pressure on its walls at the top.A little bit, but higher.
...... everything will depend on the ratio of engine thrust force to wheels friction force, the more powerful engines in relation to friction force, the less time the wheels will be overloaded and as a consequence can keep their function until the surface, otherwise the wings will lie on the runway, and born to crawl as you know can not fly :)
We neglect friction force in wheels, it is small. Nowadays, jet engines are such that they can lift an aircraft vertically.
For example, thrust of 2 engines of SU-27 is 25 tons, and an empty plane weighs 16,4 tons (with equipment - 23 tons).