Question

For International Standard Atmosphere (ISA) up to 11 km, which of the following statement(s) is/are true?

• A. The hydrostatic/ aerostatic equation is used
• B. The temperature lapse rate is taken as \(-10^{-2}\ K/m\)
• C. The sea level conditions are taken as: pressure, \(p_s = 1.01325 \times 10^5\,Pa\); temperature, \(T_s = 300\,K\); density, \(\rho_s = 1.225\,kg/m^3\)
• D. Air is treated as a perfect gas

Hint:

ISA assumes air is a perfect gas, follows the hydrostatic equation, and has a lapse rate of \(-6.5\,K/km\) up to 11 km altitude.

Answer 1

The Correct Option is A, D

Step 1: Understanding the ISA model.
The International Standard Atmosphere (ISA) is a model that defines atmospheric properties such as pressure, temperature, and density with altitude.
It uses the hydrostatic equation to relate pressure and altitude.
Step 2: Lapse rate and gas assumptions.
- The standard temperature lapse rate up to 11 km is approximately \(-6.5\ K/km = -0.0065\ K/m\), not \(-10^{-2}\ K/m\). So option (B) is incorrect.
- ISA assumes air behaves like a perfect gas (ideal gas law applies), so (D) is correct.
Step 3: Reference sea level values.
- Standard sea level pressure is \(1.01325 \times 10^5\,Pa\), temperature is \(288.15\,K\), not \(300\,K\) as in option (C), hence (C) is incorrect.