SSC JE Civil Engineering 29-Oct-2020 Shift 1 Paper

Question : 135 of 200

Marks: +1, -0

In an open channel flow, for best efficiency of a rectangular section channel, ratio of bottom width to depth shall be:

Solution:

Width of rectangular channel is b and depth of rectangular channel is y
Than Area, A = by
Perimeter, P = b + 2y

\P = (\A/\y) + 2\y

For P to be minimum,

\dP/\dy = 0

(-\A/\y^2) + 2 = 0

\A = 2\y^2

\by = 2\y^2

\b/\y = 2

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