A garden sprinkler has four rotating arms, each of which consists of Review Problems two horizontal straight sections of pipe forming an angle of 120° with each other. Each arm discharges water at a rate of 20 L/min with a velocity of 18 m/s relative to the arm. Knowing that the friction between the moving and stationary parts of the sprinkler is equivalent to a couple of magnitude M = 0.375 N . m, determine the constant rate at which the sprinkler rotates.