A tank with a square base of area $$2.0\,\text{m}^2$$ is divided by a vertical partition in the middle. The bottom of the partition has a small hinged door of area $$10\,\text{cm}^2$$. The tank is filled with water in one compartment and a liquid of relative density $$1.8$$ in the other compartment, both to a height $$5.0\,\text{m}$$. The force necessary to keep the door close is approximately. Take $$g=9.8\,\text{m s}^{-2}$$.