7класс. в водопроводе установлен кран ниже уровня воды в водонапорной башне на 15 м. вычислите давление воды на кран. с пояснениями, .

P в жидкостях= pgh, p- плотность жидкости, h-высота, g- ускор.
h=15м, p воды=1000кг/м3. 
Решение: P= 10*10^3*10*15=150000 ПА= 150кпа
ответ: 150 Кпа

Let's begin. One of the most common habits of children - a stooped posture (slouching). It is difficult to always keep your back straight (to keep the back upright) and not horbytsya (not to hump). I remember as a child I often say: "Sit up straight, and then thou shalt be like a question mark." I had to sit course. In life anything can happen. Some situations make us nervous and look for ways to throw out negative emotions. Sometimes children and adults find comfort in their nails and they start to bite (to bite nails). If for some reason they do not like nails, you can bite lips (to bite lips). Sprinkle ashes and honestly admit that he often bite the lips, especially when wonder. But nails ever!
If the situation is not critical, but just annoying us and requires our intervention nails and lips, we can "roll eyes» (to roll eyes). Not the most pleasant sight for your companion. Some people like to mash their fingers if they are thinking strongly about something or simply nothing to do. In everyday life this habit is called simply - crisp fingers, neck, back (to crack knuckles, neck, back). Doctors, incidentally, are not advised to do so.
Another, quite frankly, unpleasant action - is picking his nose (to pick your nose). What is in the nose, called boogers. On the nose and make another sniff, ie shmyhayut nose (she sniffs - it shmorhaye nose).
Another unpleasant sight - seeing a man who goes and splovuye saliva (to spit) Just feet. When this you see, includes feelings of disgust: Well, why like this? People can chew gum too loudly (to snap their gum), which is also annoying.
Do not cause approval and those in public talking on a cell phone (to talk on the phone). There are, of course, and urgent cases, but in most cases the cause of such phone calls - boredom. Another habit that occurs because of boredom or nerves - click ballpoint pen (to click a pen).

Во-первых, чтобы определить количество теплоты при ударе, нужно знать их общую скорость.

Чтобы знать общую скорость, нужно знать направление их общей скорости после столкновения. Чей импульс больше - в ту сторону и покатятся.

p1=m1*V1=6
p2=m2*V2=2

Следовательно, они покатятся в сторону тележки 1.

По закону сохранения импульса: импульс ДО равняется импульсу ПОСЛЕ.

Импульс ДО в векторном виде: m1V1+m2V2
Импульс ПОСЛЕ в векторном виде: (m1+m2)*Vобщ

Спроецируем на ось ОХ (ось направляем вправо - в сторону движения 1 тележки): m1V1-m2V2=(m1+m2)*Vобщ => Vобщ=(p1-p2)/(m1+m2)= 1 м/с

Теперь можно найти количество теплоты.

Q=дE (количество теплоты равняется "дельта" (то есть, разности начальной и конечной) энергии):

дE=Ek1-Ek2. Потенциальную энергию не учитываем, так как относительно земли тележки не меняли высоту.

Ek1=m1V1^2/2 + m2V2^2/2
Ek2=(m1+m2)*Vобщ^2/2

дЕ=m1V1^2/2 + m2V2^2/2 - (m1+m2)*Vобщ^2/2 = 6 Дж