Chapter 7, Problem 7.4P

Note: In the following problems, you will deal with both the International System of Units (SI) (N, kg, m, s, K) and the English Engineering System (lb, slug, ft, s, $°\text{R}$). Which system to use will be self-evident in each problem. All problems deal with calorically perfect air as the gas, unless otherwise noted. Also, recall that $1\text{atm}=2116{\text{lb/ft}}^{\text{2}}=1.01\times {10}^5{\text{N/m}}^{\text{2}}$.

Consider the isentropic flow over an airfoil. The freestream conditions are $T_{\infty }=245\text{K}$ and $P_{\infty }=4.35\times {10}^4{\text{N/m}}^{\text{2}}$. At a point on the airfoil, the pressure is $3.6\times {10}^4{\text{N/m}}^{\text{2}}$. Calculate the density at this point.