The mass flow rate of air through the nozzle in kg/s is

Mass flow rate, m = ρQ
where, Q = A₂ V₂
But V₂ = √2C_P(T₁ - T₂)
= √2 × 1.005 × (400 - 239.5) = 568 m/s
∴ m = 0.727 × 0.005 × 568 = 2.06 kg/s