Question

A rectangular channel is width 6 m carrier a discharge of 3 $m^3/sec$. If the width of channel is increased to 8 m, the percentage change in critical specific energy will be :

• A. no change
• B. 17.5
• C. 23.4
• D. 12.7

Answer 1

The correct option is B 17.5

For
$B_1=6m$

$(E_c{)}_1=\frac{3}{2}{y}_c$

$=\frac{3}{2}{\left(\frac{q^2}{g}\right)}^{1/3}$

$=\frac{3}{2}{\left(\frac{(3/6{)}^2}{9.81}\right)}^{1/3}$

= 0.441 m

For
$B_2=8m$,

$(E_c{)}_2=\frac{3}{2}{\left(\frac{q^2}{g}\right)}^{1/3}$

$=\frac{3}{2}\times {\left(\frac{(3/8{)}^2}{9.81}\right)}^{1/3}$

= 0.364 m

$\%changeinspecificenergy\frac{(E_c{)}_1-(E_c{)}_2}{(E_c{)}_1}$

= 0.175

= 17.55