How Much Water Flow Is Needed to Generate 780 kW from a 27m Dam?

[evenstar]

Homework Statement

A small dam produces electrical power. The water falls a distance of 27m to turn a turbine. If the efficiency to produce electrical energy is 65%, at what rate must water flow over the dam to produce 780 kW of electrical energy?

Homework Equations

v² = u² + 2as

P = $$\tau$$ x $$\omega$$

The Attempt at a Solution

I've basically been at this one on and off for a few hours, and have tied myself so completely in knots that I have no idea what I'm doing anymore. Please help someone!

 

[Carid]

Consider a litre of water going over that dam in one second.
What is its mass?
How much kinetic energy will it pick up by falling 27 metres?
The energy conversion is not totally efficent so reduce that by 35%.
Now how many litres per second do I need?