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The question states that the water does not rebound off the wall, that means the velocity of the water becomes zero, when it strikes the wall.
The momentum of the water at the mouth of pipe is : mv
The speed is zero at wall, so change in momentum is : mv
Force = rate of change of momentum
Force = mv/t
we are going to consider the force exerted on wall per second, so t=1s
F = mv --(i)
now we need to remove mass 'm' from the above equation.
density = mass/volume
p = m/V => m = p*V
volume of water = A * v
m = p * A * v <--- substitute into (i)
F = p * A * v * v
F = pAv^2
Hence the answer is D.