Answer:
 F = 1908 N
Explanation:
GIVEN,
Incident water stream has a velocity = U = +18.0 m/s,
Exiting water stream has a velocity = V = -18.0 m/s.
Mass of water per sec : M / t = 53 kg /s
Change in velocity  d v =18 m / s – ( -18 m / s) Â
                    = 36 m / s Â
Magnitude of the average force exerted on the water by the blade Â
 F = ( M / t ) x dv
   =( 53 kg /s ) x ( 36 m/s )
 F = 1908 N