physics help?

Question

A stream of water strikes a stationary turbine blade, as the drawing illustrates. The incident water stream has a velocity of +18.0 m/s, while the exiting water stream has a velocity of -18.0 m/s. The mass of water per second that strikes the blade is 20.0 kg/s. Find the magnitude of the average force exerted on the water by the blade.
___________ N

to do this do you have to find mass through the velocity, and which one.
then how would i determine acceleration to get force?

Answer 1

The change in velocity is 36 m/sec
force = dp/dt where p=mv
=20 kg/sec 36 m/sec = 720kg m/sec^2