Water flows through a convergent mouthpiece of diameter 4 cm at convergence under a head of 3 metres. If the maximum vacuum pressure is 9 metres of water, the maximum diameter of divergence, to aviod separation of flow, is

ANS:C - 2 cm

Answer is 4√2.
a1/a2= √(1+ HV/H).

a1 =area of diverging.
a2=area of converging(4 cm dia given).

H(atmosphere)- H(absolute at vena contracta) = Hv = 9m.
H = head of liquid over the mouth piece = 3m.