Force is rate of change of momentum.
F=d(Mv)/dt = d(M)/dt * v = M' * v ———————(1)
Where M' is the mass water stream flowing per second
M' is given by (density)*(volume flow rate) (M =ρV) and volume flow rate is obtained by (area of cross section)*velocity V =Av
. So we get M'=ρ*A*v
Substituting this in (1) we get
So correct option is b