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What is the torque exerted by the sea on a submerged horizontal surface?

A box with length L= 1.2 m, width W= 2 m, and height S = 1.5 m, has its top, movable surface hinged at its edge. SEE ATTACHMENT#1 for diagram.

Fig. 2 shows the box on the bottom of the ocean with its hinged top surface horizontal at distance h= 30 m beneath the surface.

The ocean density at this location is D= 1025 kg/m^3.

Find the total torque exerted by the sea water about an axis along the hinge on the horizontal hinged surface at depth h.


Solution Preview

See ATTACHMENT#2 for a diagram showing parameters.
Step 1.
The torque exerted by a force about an axis is that force times the perpendicular distance from the force line of action to the axis. Here, the axis is along the hinge. The sea exerts downward force at all points of the door, therefore ...

Solution Summary

This solution provides seven steps of calculations for determining the density, pressure and element of torque. This solution is also attached as a PDF file.