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# What is the Kinetic Energy of water from a dam?

I have this question for physics homework, I can get a and d I think but I can't work out how to go about b and c.

In a damn water falls 30m to the turbine below.

a) What is the kinetic energy of 5 kg of water just before it hits the turbine?

I said KE=1/2 mv2

KE= 1/2 x 5 x30 2

KE= 2250 J

b) Assuming 100% efficiency in converting kinetic energy to electrical power at what rate (kg per sec) must water flow through the power station to provide 10 megawatts of electrical power?

c) What must water flow through the power station to provide 10 megawatts of electrical power if the power station worked at 90% efficiency?

d) Water flow rates are normally given in cubic meters per second. Convert your answers in b and c

### 1 Answer

- ZardozLv 79 years agoFavorite Answer
For" a" you replace "v", velocity, in the fromula with "h", hight of drop, a distance.

Instead use U = mgh, knowing that the potential energy converts to an equal quantity of KE.

5 kg • 9.8 m/s^2 • 30 m = 1470 kg (m/s)^2 = 1470 J

For "b" remember that a Watt = J/s, and that 5 kg/s = 1470 J/s.

For "c" divide "b" by 0.9