Given:

$D_{1}=200 mm=0.2m$

=400mm=0.4m

N=1200rpm

Vane angle at inlet $\phi=2o^{\circ}$

Vane angle at outlet =$\phi=30^{\circ}$

Radical on try i.e $\alpha=90^{\circ}$

$Vw_{1}$=0

$vf1$=v1

$u1=\frac{\pi D_{1}N}{60}$

$\frac{\pi \times 0.2\times 1200}{60}$

=12.57 m/s

u2=$\frac{\pi D_{2}N}{60}$

=$\frac{\pi\times 0.4\times 200}{60}$

=25.13 m/s

$\frac{Vf1}{u1}=tan\Theta$

$\frac{vf_{1}}{12.5 x}=tan20$

vf1=4.575 m/s=vf2

Consider outlet velocity $\triangle$EFG

$Vw2=EF-HF=u2-\frac{Vf2}{tan\phi}=25.13-\frac{4.575}{tan 30}$=17.21 m/s

Workdone by impeller/unit weight of water w

w=$\frac{Vw_{2}\times u2}{g}$

=$\frac{17.21\times 25.13}{9.81}$

=44.09 Nm/Ng water