A 20 cm diameter 500 m long water ripe with friction factor $u_{f}$ = 0025, leads from a constant-head reservoir and terminates at the delivery end into a nozzle discharging into air. (Neglect all energy losses other than those due to pipe friction). What is the approximate diameter of the jet for maximum power?
a. 6.67 mm b. 5.98 mm
c. 66.7 mm d. 59.8 mm