# Homework Help: Hydroelectric generation and energy question?

1. Nov 8, 2012

### bohobelle

1. The problem statement, all variables and given/known data
Imagine that all the electricity used in an average home comes from hydroelectric generation. Your task is to estimate the annual average rate at which water would need to flow to generate the power for that home (gallons per minute or cubic meters per second). Make your estimates using a hydro system that is 90% efficient and in which the lake level is 20 m above the generator. Hydro plants work by converting GPE stored in the water to KE as it falls and turns a turbine.
The average household uses 8,900 kWh of electricity each year or 32,040,000,000 J per year.
The desnity of water is 1000 km/m^3, and the lake is 20m above the generator. Hydro plants convert GPE stored in water to KE as it falls and turns a turbine.

2. Relevant equations

3. The attempt at a solution
I honestly have no idea where to start with this equation. My professor has never gone over anything remotely like this in class, so I honestly do not know where to start!

2. Nov 8, 2012

### Staff: Mentor

What is the Relevant Equation relating the change in potential energy PE to the mass of an object and how far it falls? You've covered that, I'd bet.

How much does a cubic meter of water weigh?

How much PE is lost if a cubic meter of water falls 20m?

Factor in the 90% efficiency...

How much energy per cubic meter of water falling can you convert into electricity?

And so on...