A vessel closed with a cork, the weight of which is equal to the buoyancy force, rests at the bottom of a glass of water. Almost without doing work, it can be raised to the surface of the water. If you remove the plug now, the sovud will fill with water and drown. In doing so, he can do the job. If the cork is removed while the vessel is at the bottom, it will also fill with water, but it will not do the job. How to reconcile the gain obtained in the first case in work with the energy conservation law?
In the first case, water flows into the vessel more slowly than in the second, because the pressure at the surface is less than at the bottom; further, the vessel is lowered by gravity. As a result, the change in energy is spent on increasing the internal energy of the water and the vessel. The kinetic energy of water in the second case is converted into the internal energy of water, the change in which will be greater than in the first case.
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