A mass of gas at an initial pressure of 28 bar and with an internal energy of 1500 kJ, is contained in a well-insulated cylinder of volume 0.06 m³. The gas is allowed to expand behind a piston until its internal energy is 1400 kJ; the law of expansion is PV²=Constant. Calculate
1. Work done;
2. The final volume;
3. The final pressure;
4. Draw P-V diagram.