3.77 A plug in the shape of a hemisphere is inserted in a hole in the side of a tank as shown in the figure. The plug is sealed by an O-ring with a radius of 0.2 m. The radius of the hemispheri- cal plug is 0.25 m. The depth of the center of the plug is 2 m in fresh water. Find the horizontal and vertical forces on the plug due to hydrostatic pressure. O-ring 0.2 m 0.25 m PROBLEM 3.77 2 m 3.93 Determine the minimum volume of concrete (y = 23.6 kN/m²) needed to keep the gate (1 m wide) in a closed position, with 2 m. Note the hinge at the bottom of the gate. Water Submerged concrete block PROBLEM 3.93 Stop Hinge