With the assumptions of Example 18.4 (Section 18.1), at what altitude above sea level is air pressure 90% of the pressure at sea level?

Solution 17E Step 1: The calculation in example 18.4 shows, the pressure decreases exponentially with the increase in altitude. P = P e0p ( Mgy / RT)-----------------(1) At the sea level the pressure is 1.013 × 10 Pa. The pressure must be 90 %of the pressure at the sea level. So, the pressure will be, 1.013 × 10 Pa × 90 % = 0.9117 × 10 Pa. 5 Step 2: By putting this pressure in equation 1 we can get the height or the y value. 5 P = P e0p ( Mgy / RT) = 0.9117 × 10 Pa 5 5 1.013 × 10 exp ( Mgy / RT) = 0.9117 × 10 exp ( Mgy / RT) =(0.9117 × 10 ) / (1.013 × 10 ) = 0.9 y = 0.105 / (Mg / RT) = 0.105 RT / Mg