a storage tank has a diameter of 80 ft, a height of 25ft and contains oil to a height of 15ft. the suction pumps, which can handle 15000bbl/d, are started, but the safety valves are clogged and a vacuum is drawn in the tank. the roof is flat and rated to withstand 1.0 oz/sq in. before collapsing. the barometer pressure is 30 in Hg. how long will it takes the tank to collapse? what is the total force on the roof at collapse? how woould more oil in the tank have affected the collapse time?