I have the exact same question, any chance you figured it out since you posted this?
I uploaded the answer to a file hosting. Here's link:
tinyurl.com/wpazsebu
Answer:
The average force exerted by the water on the ground is 17.53 N.
Explanation:
Given;
mass flow rate of the water, m' = 135 kg/min
height of fall of the water, h = 3.1 m
the time taken for the water to fall to the ground;

mass of the water;

the average force exerted by the water on the ground;
F = mg
F = 1.789 x 9.8
F = 17.53 N
Therefore, the average force exerted by the water on the ground is 17.53 N.
The answer is B- Perfect Cosmological Principle
Sorry it took people so long to anser:)