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Water flows through two identical tubes A and B. In a given time, a volume V0 passes through tube A and 2*V0 passes through tube B. Which of the following could be correct?
- The flow in both tubes is steady (laminar).
- The flow in both tubes is turbulent.
- The flow is steady in A but turbulent in B.
- The flow is steady in B but turbulent in A.
Correct answer: The flow is steady in A but turbulent in B.
Solution
For identical tubes, the flow speed is proportional to volume flow rate. Reynolds number Re = rho*v*D/eta increases with speed. B carries twice the flow of A, so B has the larger Re. Depending on the values, B can exceed the critical Re (turbulent) while A stays below it (steady/laminar). The combination 'turbulent in A but steady in B' is impossible because B is faster. Hence the consistent possibility is steady in A and turbulent in B.
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