The 'Mach number' becomes important in fluid mechanics when:
Choose the correct answer
In all flow of water regardless of velocity
When V approaches speed of sound (Ma > 0.3) — density changes significant; not usually relevant in water flow or low-speed air
Only for laminar flow
When Reynolds number exceeds 10⁶
Correct Answer
B. When V approaches speed of sound (Ma > 0.3) — density changes significant; not usually relevant in water flow or low-speed air
AI Detailed Explanation & IS Code Reference
Unlock the reasoning, formula path and code-linked notes inside your student dashboard.
Mach number Ma = V/c where c = speed of sound = √(γRT) for ideal gas. Ma < 0.3: incompressible flow (density changes < 5%, can ignore). Ma 0.3–0.8: subsonic compressible. Ma ~ 1.0: transonic. Ma > 1.0: supersonic (shock waves). Ma > 5: hypersonic. Civil engineering: almost all applications use water or slow air → Ma << 0.3 → incompressible → Mach number irrelevant. Relevant in: pneumatic conveying, gas pipelines at high velocity, aerodynamic forces on tall buildings in special cases.
ScoreCardAI links this solution with subject, topic and difficulty signals so your scorecard can identify weak areas after a full mock test.
Practice more Civil Engineering questions
This MCQ belongs to JE Level Premium Test Series. Full tests include timed attempts, rank comparison and subject-wise analysis.