Class Exercise 1 – Pressure and Temperature
1. A vacuum gauge indicates that the pressure of air in a rigid vessel is 0.2 bar
(vacuum). The pressure of the atmosphere is equivalent to 750 mm column of
mercury. Given: Density of mercury is 13.59 g/cm3.
i. Sketch the system with appropriate labels.
ii. Determine the atmospheric air pressure, in bar.
iii. Calculate the absolute pressure of the air in the vessel, in kPa.
(Ans: 1 bar; 80 kPa)
2. A gas is contained in a vertical, frictionless piston-cylinder device, as shown in
Figure 1.1. The piston has a mass of 4 kg and cross sectional area of 35 cm2.
A compressed spring above the piston exerts a force of 60 N on the piston. If
the atmospheric pressure is 95 kPa, determine the absolute pressure inside
the cylinder.
(Ans: 123.35 kPa)
Figure 1.1
3. The gage pressure of the air in the tank shown in Figure 1.2 is measured to
be 65 kPa. Determine the differential height h2 of the mercury column.
(0.47 m)
Figure 1.2
60 N
Patm = 95 kPa
mp = 4 kg
A =35 cm
2
Air
Water
Oil
SG = 0.72
Mercury
SG = 13.6
h1=30 cm
h2
h3 =75 cm
65 kPa
