Physics---thermodynamics1

Let Eo be the internal energy at state B.

From B --> C, work done by the gas = 3x10^5 x (0.4-0.09) J = 93000 J = 93 kJ
From the first principle of thermodynamics, dQ = dU + dW
100 = dU + 93
dU = (100 - 93) kJ = 7 kJ
hence, internal energy of the system at C = (Eo + 7) kJ

At state D, internal energy = (Eo + 7) kJ because the gas expands under constant temperature (isothermal) situation.

From D --> A, work done by the gas = 10^5 x (0.2 - 1.2) J = -10^5 J = -100 kJ
hence, -150 = dU - 100
dU = (100 -150) kJ = -50 kJ
hence, internal energy at state A = (Eo + 7 - 50) kJ = (Eo - 43) kJ

The difference in internal energy between A and B = 43 kJ