2. A barrel 1.5 meters high is completely filled with water and covered with a lid. The mass of the water in the barrel is 1000 kg. A long thin tube with a cross-sectional area of $1 \mathrm{~cm}^{2}$ is inserted vertically into the lid of the barrel, which is completely filled with water. Find the length of the tube if it is known that after it is filled, the pressure at the bottom of the barrel has doubled. The density of water is 1000 kg $/ \mathbf{M}^{3}$.
Answer: 1.5 m. Solution. To solve the problem, you only need to know how pressure changes with depth: $p=\rho g$. From this relationship, it follows that to double the pressure, you need to double the height of the liquid column. This means that the tube should be the same height as the barrel - 1.5 m.