A tank with a square base of area 1.0 `m^2` is divided by a vertical partition in the middle. The bottom of the partition has a small-hinged door of area 20 `cm^2`. The tank is filled with water in one compartment, and an acid (of relative density 1.7) in the other, both to a height of 4.0 m. compute the force necessary to keep the door close.