1. The problem statement, all variables and given/known data How to show that the dE/dy = 0 , yc will become (Q^2 / g)^1/3 ??? http://www.brighthubengineering.com...nnel-flow-basics-2-supercritical-flow/#imgn_0 2. Relevant equations 3. The attempt at a solution E = y + (V^2) /2g , dE / dy = 1 ... why yc will become (Q^2 / g)^1/3 ???