The 'momentum equation' for hydraulic jump in a rectangular channel gives:
Choose the correct answer
Energy equation only (no momentum needed)
Sequent depth ratio: y2/y1 = 0.5(-1+√(1+8Fr1²)) from continuity + momentum (energy is dissipated so not used directly)
Darcy-Weisbach formula for friction
Only upstream depth and slope
Correct Answer
B. Sequent depth ratio: y2/y1 = 0.5(-1+√(1+8Fr1²)) from continuity + momentum (energy is dissipated so not used directly)
Why is this the answer?
Hydraulic jump: continuity + momentum (Belanger). Momentum: γQ(V2-V1)/g = γy1²/2 - γy2²/2 per unit width. Combining with continuity Q=Vy: y2/y1 = 0.5(-1+√(1+8Fr1²)). Energy dissipated: ΔE = (y2-y1)³/(4y1y2). Only continuity + momentum needed (energy lost but unknown). This is why momentum used, not energy for jump analysis.
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