[Archive!] Pure mathematics, physics, chemistry, etc.: brain-training problems not related to trade in any way - page 22
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Вы хотите спросить, сколько весит сосуд?
Hail to the bearI'll say it again. The plane will take off. A plane with flies weighs the same as one with landed flies.
By the way, you're confusing weight with mass. These are different things.
OK, another experiment. There's a loaded gun firing pellets without gunpowder. It stands on a scale. It weighs a ton.
Now it has fired. The baton weighs 100 kilograms. It has flown upwards of a kilometre. The scales have calmed down from the shot during this time. How much do they show? Apparently 900 kilograms.
Now enclose that entire kilometre in a sealed vessel. It'll be the same 900 while the dummy is in the air. But when the dummy falls, it will be a ton again (when the scales calm down).
The mass of "all together" will not change in any way, it will be 1000 kg.
Unless you count gunpowder.
Would a plane with a ton of flies in it take off if at the moment/moments of lift-off they were simultaneously landing?)
A closed system with its own internal energy is weighed. The total energy (read - mass) does not change from the movement of the components within the system. There is no difference in what is being pressed inside the system.
The general conclusion is correct, but the reasoning is not quite.
It's the usual static. The internal energy has nothing to do with it. There is an elementary condition of equilibrium of forces. It's the weight of the plane and the air inside that weighs on the scales. And what makes the flies fly? What compensates for their weight? The air. They rest on the air with their wings. So the air presses the scales with the weight + the pressure of the flies (=the weight of the flies).
As for Alexey's example, it does not change the situation. Except for one small thing: the problem from static becomes dynamic. Readings of the weights become a function of time. The question must be posed with an indication of a point in time. And the answer will be: at the moment of a shot the scales will show total weight + force with which the gases in the cannon barrel push the shell, after the shot ... etc.
i.e. the plane will take off??????!!!!!!
And won't even give it a second thought. :-)
Общий вывод правильный, но аргументация не совсем.
Это обычная статика. Внутренняя энергия тут ни при чем. Есть элеиентарное условие равновесия сил. На весы давит вес самолета и воздух внутри него. А за счет чего мухи летают ? Что компенсирует их вес ? Воздух. Они опираются о воздух своими крылышками. Так что воздух давит на весы с силой вес+сила давления мух.
Что касается примера Алексея, то он ситуацию не меняет. Кроме одной малости: задачка из статической становится динамической. Показания весов становятся функцией времени. Вопрос надо задавать с указанием момента времени. И ответ будет таков: в момент выстрела весы будут показыывать общий вес + силу, с котрой газы в стволе пушки толкают снаряд, после выстрела ... и т.п
I managed to write the post above about the dynamics.
И даже не задумается. :-)
Yuri, have you ever tried walking up an escalator to meet the movement of the belt? Do you accelerate much? You don't take off? :о))) (kind of a joke)
I managed to write the post above about the dynamics.
Yes, while I was writing. :-)