11.30 A plate of negligible weight closes a 1-ft-diameter hole in a tank containing air and water as shown in Fig. P11.30. A block of concrete (specific weight =150 lbf/ft3), having a volume of 1.5 ft3, is suspended from the plate and is completely immersed in the water. As the air pressure is increased, the differential reading, h, on the inclined-tube mercury manometer increases. Determine h just before the plate starts to lift off the hole. The weight of the air has a negligible effect on the manometer reading.
