# physics

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Approximately 5.5 X10^6 kg of water fall 50m over Niagara Falls each second.
a) What is the decrease in the gravitational potential energy of the water-Earth system each second?
b) If all this energy could be converted to electrical energy (canâ€™t happen) at what rate would electrical energy be supplied? (the mass of 1 m^3 of water is 1000kg)
c) If the electrical energy were sold at 1 cent/kW *h what would be the yearly cost?

a)would I use 1/2mv^2=mgh? But the thing is velocity isn't given.
For b) and c) confuses me could you please guide me into the right direction?

• physics -

Sorry, I know this is 5 years late, however:

For a) you would use the potential energy equation: mgh

For b) you would use the power equation: Ep(answer from question a))/1s
This answer should be practically the same as answer a), what you've done in question b) is changed the units. (From Joules to Watts)

For c) you would multiply your answer from b) by the total hours per year and divide that product by 1000W (to find kW).
After this you'll have cents per year, however your yearly cost or income should be in dollars per year. In order to find this simply divide your cents total by 100 cents to find dollars.