Answer:
[tex]6400\ \text{N}[/tex]
Step-by-step explanation:
[tex]\dfrac{m}{t}[/tex] = Mass flow rate of water = 320 kg/s
[tex]m[/tex] = Mass of water on the door
[tex]t[/tex] = Time
[tex]v[/tex] = Velocity of water on the door = 20 m/s
Force is given by
[tex]F=\dfrac{m}{t}v\\\Rightarrow F=320\times 20\\\Rightarrow F=6400\ \text{N}[/tex]
The average force is exerted by the stream of water is [tex]6400\ \text{N}[/tex].