Problem 4-B The flow of water from a reservoir is controlled by a 9 ft-wide L-shaped gate hinged at point A. If it is desired that the gate open when the water height is 30 ft, determine the mass of the required object W at point B. (Hint: Calculate the water pressure force and its line of action on the gate, and then use the moment equilibrium about the hinge A to determine the mass of W at point B.) 16 ft W A B 1 = 5 ft FR h=30 ft