Question $1$:

$(8+2$ grade$)$

Consider a river flowing toward a lake at an average and a specified velocity of $3\frac{m}{s}$ at a rate of $100\frac{m^3}{s}$ at a location $90m$ above the lake surface. Determine the total mechanical energy of the river water per unit mass and the turbine efficiency, when the power output is $1100KW.$