A gas of mass 1.5 kg undergoes a quasi-static expansion which follows a relationship p = a + bV where a and b are constants. The initial and final pressure are ${10}^{3}kPa$  and 200 kPa and corresponding volumes are $0.2m^3$  and $1.2m^3$ . The specific internal energy of the gas is given by $U=1.5pV-85kJ/kg$ (where P is in kPa and V in $m^3/kg$ ):-