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in Thermodynamics by (20 points)
A supersonic plane flies at 2000 km/hr at an altitude of 9 km above sea level in standard atmosphere. If the pressure and density of air at this altitude are to be 30 KN/m² absolute and 0-45 kg/m³, calculate pressure, temperature and density at the stagnation point on the nose of the plane. Take R 287 J/kg/k and y = 1.4.

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Sonic velocity

 \(\alpha=\sqrt{\gamma RT}=\sqrt{\gamma (p/\rho)}=\sqrt{1.4\times30\times10^3/0.45}=305.5\,m/s\)

Speed of plane 

V = 2000 km/hr = \(\frac{2000\times10^3}{3600}=555.56\,m/s\)

Mach number M \(=\frac{V}{\alpha}=\frac{555.56}{305.5}=1.818\)

From characteristic gas equation, \(\frac{P}{\rho}=RT\)

Temperature \(T=\frac{P}{\rho\,R}=\frac{30\times 10^ 3}{0.45\times287}=233.3\,K\)

Stagnation pressure, 

\(P_0=P\left(1+\frac{\gamma -1}{2}M^ 2\right)^{\frac{\gamma}{\gamma -1}}\)

\(=30\left(1+\frac{1.4-1}{2}\times 1.818^2\right)^{\frac{1.4}{1.4-1}}=177.19\,KN/m^ 2\)

Stagnation temperature, 

\(T_0=T\left[1+\frac{\gamma -1}{2}M^ 2\right]=233.3\left[1+\frac{1.4-1}{2}\times1.818^2\right]=387.5\,K\)

Stagnation density,

\(\rho _0 =\frac{p_0}{RT_0}=\frac{177.19\times 10^3}{287\times 387.5}=1.583\,Kg/m^3\)

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