GATE 2025 AE – Question 21

Aerodynamics · Basic fluid mechanics: kinematics, conservation laws, dimensional analysis, incompressibility and Newtonian fluids · 1 mark · Multiple choice

In a fluid flow, Mach number is an estimate of _____.

$\sqrt{\frac{\text{inertia force}}{\text{viscous force}}}$
$\sqrt{\frac{\text{inertia force}}{\text{elastic force}}}$
$\sqrt{\frac{\text{elastic force}}{\text{viscous force}}}$
$\sqrt{\frac{\text{viscous force}}{\text{inertia force}}}$

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Correct answer: (B) $\sqrt{\frac{\text{inertia force}}{\text{elastic force}}}$

Explanation

The Mach number $M = \frac{V}{a}$ satisfies $M^2 = \frac{\rho V^2}{\rho a^2} = \frac{\text{inertia force}}{\text{elastic (compressibility) force}}$, so $M$ is the square root of that ratio.