Q1.Water sprinkler used for grass lawns begins to rotate as soon as the water is supplied.Explain the principle on which it works.
Q2.An iron sphere of mass 1Kg is dropped from the height of 10m.If the acceleration of sphere is 9.8m/s square.Calculate the momentum transferred to the ground by the ball.

Dear Student ,
(1) It is based on the third law of motion which states that for every action there is an equal and opposite reaction. As the water comes out of the sprinkler, an equal and opposite reaction force comes into play. So the sprinklers start rotating.
(2)
m = 1 kg

u = 0 (as it is dropped from rest)

g = 10 m/s²

h =10m

v²-u²=2gh

v² - 0 = 2 x 1 x 10 = 20

v= 4$\sqrt{5}$m/s

Now, as the ball stops after collision from ground, we can assume that all of it's momentum gets transferred to the ground.

So

Momentum transferred = Final Momentum = m v = 1 x 4$\sqrt{5}$ = 4$\sqrt{5}$ kg m/s 
Regards