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The critical flow condition in a channel is given by ________.
[Note: α – kinetic energy correction factor; Q – discharge; A_c – cross-sectional area of flow at critical flow condition; T_c – top width of flow at critical flow condition; g – acceleration due to gravity]
- αQ²/g = A_c³/T_c
- αQ/g = A_c³/T_c²
- αQ²/g = A_c³/T_c²
- αQ/g = A_c³/T_c
Correct answer: αQ²/g = A_c³/T_c
Solution
At critical flow the Froude number is unity, giving the condition alpha*Q^2/g = A_c^3/T_c (equivalently alpha*Q^2*T_c/(g*A_c^3) = 1). The exponents on A and the single power of T_c distinguish the correct form.
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