Tutorial No-3- Work and Heat

Tutorial No-3-( Work and Heat)

Q1/In the system shown (fig.1), the piston has a negligible weight and the initial spring force is zero. The gas is heated until the volume is doubled and the final pressure is 5bar. Calculate the work done on spring and the total work done . Ans.(100kJ, 300 kJ)

Q2/ A gas is contained in a piston cylinder arrangement as shown in fig 2. The spring has a constant of 105 N/m maintains the gas in mechanical equilibrium. Heat is transferred to the gas at a slow rate so that the pressure and temperature are always uniform through the gas. Calculate the work done by the gas during the process when the pressure changes from 1 bar to 3 bar assuming that the piston cross sectional area is 0.1 m2.

Q3/ The pressure inside a balloon is 100 Kpa until the volume becomes 20 m3 after that the relationship between pressure and volume becomes P=P0+C(V-V0)2 where P0=100 Kpa, V0=20m3 The balloon contains helium at 100 Kpa and 20 0C and the volume is 15 m3. The balloon is heated until 400 0C and 150 Kpa. Calculate the work done by helium.

Q4/ The driver of 1350 kg car moving down a hill sees a red light at a traffic junction at the bottom of the hill where he must stop. The speed of the car at the time the brakes are applied is 28 m/s and the car is at 30 m vertically above the bottom of the hill. How much energy is dissipated as heat if the wind and other frictional losses are neglected. Ans.(926.36kJ)

Q5/ A piston cylinder device contains helium gas initially at 150 kpa, 20 0C, and 0.5m3. The helium is now compressed in a polytropic process (PVn=C) to 400 kpa and 140 0C. determine the heat transfer for this process.