Examples

A mass of 2.4 kg of air at 150 kPa and 12°C is contained in a gas-tight, frictionless piston-cylinder device. The air is now compressed to a final pressure of 600 kPa. During the process, heat is transferred from the air such that the temperature inside the cylinder remains constant. Calculate the work input during this process

Example2 A piston-cylinder device contains 50 kg of water at 150 kPa and 25°C. The cross-sectional area of the piston is 0.1 m 2 . Heat is now transferred to the water, causing part of it to evaporate and expand. When the volume reaches 0.2 m 3, the piston reaches a linear spring whose spring constant is 100 kN/m. More heat is transferred to the water until the piston rises 20 cm more. Determine (a) the final pressure and temperature and (b) the work done during this process. Also, show the process on a P-Vdiagram

Example 3 A piston-cylinder device with a set of stops contains 10 kg of refrigerant-134a. Initially, 8 kg of the refrigerant is in the liquid form, and the temperature is 8°C. Now heat is transferred slowly to the refrigerant until the piston hits the stops, at which point the volume is 400 L. Determine (a) the temperature when the piston first hits the stops and (b) the work done during this expansion process. Also, show the process on a P-Vdiagram.

Example 4 Determine the work required to deflect a linear spring with a spring constant of 70 kN/m by 20 cm from its rest position

Example 5 Determine the power required for a 2000-kg car to climb a 100-m-long uphill road with a slope of 30°(from horizontal) in 10 s (a) at a constant velocity, (b) from rest to a final velocity of 30 m/s, and (c) from 35 m/s to a final velocity of 5 m/s. Disregard friction, air drag, and rolling resistance.

Example 6 Steam is leaving a pressure cooker whose operating pressure is 30 psia. It is observed that the amount of liquid in the cooker has decreased by 0.4 gal in 45 minutes after the steady operating conditions are established, and the crosssectional area of the exit opening is 0.15 in 2 . Determine (a) the mass flow rate of the steam and the exit velocity, (b) the total and flow energies of the steam per unit mass, and (c) the rate at which energy is leaving the cooker by steam