Question

Consider a river flowing toward a lake at an average velocity of 3 m/s. the river height is 90m above the lake. what is the total mechanical energy of the river water per unit mass in kj/kg?

Answer 1

Kinetic energy per unit of mass is

$K=\frac{v^{2} }{2}$

Given, $v=3m/s^{2}$

Therefore,

$K=\frac{(3^{2} m/s^{2} )^2}{2}$

$K=4.5 J/kg$

Now potential energy per unit mass is

$p=g\times h$

Given, $h=90 m$

Therefore,

$p= 9.8m/s^2 \times 90$

$p=882.9 J/kg$

Thus, total mechanical energy of the river water per unit mass is

$T=K+p=(4.5+882.9)J/kg$

$T=887.9 J/kg$

OR

$T=0.887 kJ/kg$