An underwater sea tunnel is maintained at an internal pressure of 1 atmosphere. In the roof of the tunnel there are escape hatches of mass 30 kg and of diameter 3 m2. At a depth of 50 m what force must be applied to open an escape hatch (assuming it opens upwards into the water) . Assume the density of sea-water is 1000 kg/m3 , the acceleration due to gravity is 9.8 m/s2 and that atmospheric pressure is 1.01x105 Pa.
