$(40)$ A channel of rectangular section, $4ft$ wide, is discharging water at a rate of $50f\frac{t^3}{s}$ with an average velocity of $2\mathrm{.}5f\frac{t}{s}.$

Find $($a$)$ the specific energy of the flowing water,

$($b$)$ type of flow $($super$,$ sub or critical$)?$

$($c$)$ depth of water when the specific energy is minimum,

$($d$)$ velocity of the water when the specific energy is minimum,