The average flow rate in the niagara river is 6.0 × 106 10. kg/s, and the water drops 50 m over niagara falls. if all this energy could be harnessed to generate hydroelec- tric power at 90% efficiency, what would be the electric power output?

Explanation:

The power produced by the water falling down the Falls is

where

E = mgh is the potential energy of the water, with m being the mass, g the gravitational acceleration, h the height

t is the time

In this problem we have

us the mass flow rate

h = 50 m is the height

g = 9.8 m/s^2 is the acceleration of gravity

Substituting,

And since the efficiency is only 90%, the power output is

a lot of it means it can be "burned" for energy and sold at one price. if it is scarce, the price will go up

air exerts forces on falling objects near earth’s surface.

explanation:

the term 'free falls' refer to object that are falling towards the earth, in a situation in which gravity is the only force acting on the object.

for an object in free fall, the acceleration is constant (g, the gravitational acceleration), and so the velocity of the object constantly increases.

for objects near earth's surface, there is always another force acting on the object: the resistance due to the air. this force is opposed to the direction of fall of the object, and it is proportional to the velocity of the object, so as the object falls down, this force increases up to a point when it balances the force of gravity, and the object continues its motion at constant velocity (called terminal velocity). since in this case gravity is not the only force acting on the object, we are not in a situation of free fall.