Question

A 3.0-cm-diameter tube is held upright and filled to the top with mercury. The mercury pressure at the bottom of the tube − the pressure in excess of atmospheric pressure-is 48 kPa. How tall is the tube?

Answer 1

Given a tube of diameter d, = 3cm = 0.03m

Pressure Balance

Mercury pressure at the tube bottom Pₓ = Pa + ρgh

where

Pa = Atmospheric pressure = 101kpa

ρ = Density of mercury = 13,546kg/m3

g = acceleration due to gravity

h = height of the tube?

Given

Bottom pressure in excess of the atmospheric pressure = 48kPa = Pₓ - Pa

Therefore, 48kPa = ρgh

h = 48(kN/m2)/ρg

h = 48,000kgms⁻²m⁻²/(13546kgm⁻³ x 9.81ms⁻²)

h = 0.36m

the tube is 36cm tall