Answer
$F=1100N$
Work Step by Step
$r_1=0.035m$
$r_2=0.00375m$
$\frac{V}{t}=Av$
$420\frac{L}{min}\times\frac{1m^3}{1000L}\times\frac{min}{60s}=0.007\frac{m^3}{s}$
$\frac{m}{t}=\frac{m}{V}\times\frac{V}{t}=1000\frac{kg}{m^3}\times0.007\frac{m^3}{s}=7.0\frac{kg}{s}$
$v_1=\frac{V}{tA_1}=1.82\frac{m}{s}$
$v_2=\frac{V}{tA_2}=1.58\times10^2\frac{m}{s}$
$F=ma=m\frac{v}{t}=7.0\frac{kg}{s}\times(v_2-v_1)=1100N$