Q.

A liquid of density 600 kg/m3 flowing steadily in a tube of varying cross-section. The cross-section at a point A is 1.0 cm2 and that at B is 20 mm2. Both the points A and B are in same horizontal plane, the speed of the liquid at A is 10 cm/s. The difference in pressures at A and B points is ______ Pa.              [2026]

1 18  
2 144  
3 36  
4 72  

Ans.

(4)

Using continuity equation,

AAVA=ABVB

1×10=0.2×VB

⇒VB=50 cm/s=0.5 m/s

PA+12ρvA2=PB+12ρvB2

PA-PB=12ρ(vB2-vA2)

PA-PB=12×600×((0.5)2-(0.1)2)

⇒PA-PB=72