A mercury manometer (/rhorho = 13,600 kg/m^3) is connected to an air duct to measure the pressure inside. The difference in the manometer levels is 30 mm, and the atmospheric pressure is 100 kPa.

(a) Determine if the pressure in the duct is above or below the atmospheric pressure.

(b) Determine the absolute pressure in the duct.

A) The pressure is below atm pressure

B) Pabs = 96 kPa

Explanation:

Pressure exerted by mercury = pgh

Where: p = density (13600 kg/m^3)

g = acceleration due to gravity 9.81 m/s^2

h = level difference within manometer = 30 mm = 30x10^-3 m

Pressure = 13600 x 9.81 x 30x10^-3

= 4002.43 Pa = 4.00243 kPa

This is below atmospheric pressure

Absolute pressure is calculated as:

Pabs = Pg + Patm

Pabs = - 4 + 100 = 96 kPa