Air flows adiabatically through a horizontal duct and at a section numbered (1) the static pressure p1= 150 kPa, the static temperature T1 = 200°C and the velocity c1 = 100 m/s. At a station further downstream the static pressure p2= 50 kPa and the static temperature T2= 150°C. Determine the velocity c2 and the change in entropy per unit mass of air. For air take R = 287 J/(kg K) and γ 5 1:4.