Hot air (at 50 °C) is contained in a piston–cylinder arrangement as shown in the sketch for Problem 2.54. 

The volume of the air is 250 cm³. The piston has a diameter of 4 cm and a mass of 49 kg. The gas forces on each side of the piston, assuming there are no frictional forces at the piston–cylinder interface, balance the weight of the piston. Determine the absolute pressure of the air (kPa) and the mass of air in the cylinder (kg). The atmospheric pressure is 98 kPa. Assume standard gravity.

Problem 2.54

A piston–cylinder assembly (see sketch) contains 0.005m³ air at 29.4  °C. The gas forces on each side of the piston, assuming there are no frictional forces at the piston-cylinder interface, balance the weight of the piston. The piston has a cross-sectional area of 20.2 in² and a mass of 160.6 kg. The local gravitational acceleration is 9.144m/s². Determine the mass of air trapped within the cylinder. The atmospheric pressure is 101.35 kPa.