A thin 4-ft-wide, right-angle gate with negligible mass is free to pivot about a frictio...

A thin 4-ft-wide, right-angle gate with negligible mass is free to pivot about a frictionless hinge at point O, as shown in Fig. P2.56. The horizontal portion of the gate covers a1-ft-diameter drain pipe, which contains air at atmospheric pressure. Determine the minimum water depth, h, at which the gate will pivot to allow water to flow into the pipe.