Density and Pressure
Example 1
Example 2
Example 3
Example 4
Example 5
Example 6
Example 7


Density and Pressure in Fluids
Example 7


Fig 1

The U-tube in Fig 1 contains two liquids in static equilibrium exposed to the atmosphere. Water is in the left arm, and liquid of unknown density is in the right. The water surface is 18 cm above the horizontal line XY and the unknown liquid is 20cm above the same line.
(a) What is the density of the unknown liquid?
(b) ) If the U-tube is used as a manometer to measure gas pressure, what would be the gas pressure if the liquid levels are 10m vertical difference?
Density of water = 1.00 X 103 kgm-3
Atmospheric Pressure = 1.01 X 105 Pa

(a) Pressure of the water at A = Atmospheric Pressure + ρwghw ---Eq1
Pressure of the unknown liquid at B = Atmospheric Pressure + ρughu ---Eq1

Since the liquids are in static equilibrium the pressure is the same
Pressure of the water at A = Pressure of the unknown liquid at B
∴ Atmospheric Pressure + ρwghw = Atmospheric Pressure + ρughu
ρwhw = ρuhu
ρu= (ρwhw) / (hu)
ρu= [(0.18 m X 1.00 X 103 kgm-3) (0.20 m) /]
ρu= 9 X 102 kgm-3

Pressure at A = Pressure at B.
Pressure at B = Atmospheric Pressure + ρLghL
Pressure at B = (1.01 X 105 Pa) + [(9 X 102 kgm-3) X (10 ms-2 X 10m)]
Pressure at B = 1.91 X 105 Pa

Concept by Kishore Lal. Programmed by Kishore Lal... Copyright © 2015 Kishore Lal. All rights reserved.