# Waterfall Energy Question

1. Nov 21, 2009

### tamir102

1. The problem statement, all variables and given/known data

The highest waterfall in Canada is the Della Falls in British Columbia, with a change
in elevation of 4.4  102 m. When the water has fallen 12% of its way to the bottom,
its speed is 33 m/s. Neglecting air resistance and fluid friction, determine the speed
of the water at the top of the waterfall.

2. Relevant equations

E before = E after
1/2 mv^2 + mgh = 1/2 mv^2 + mgh
v^2 + 2gh = v^2 + 2gh
v^2 = v^2 + 2gh - 2gh
v = √v^2 + 2gh - 2gh

3. The attempt at a solution

GIVENS:

waterfall distance from ground = 440m
V2= 33m/s
water fallen at 12% distance = 387.2m

v = √v^2 + 2gh - 2gh
v = √(33m/s)^2 + 2(9.8 m/s^2)(387.2m) - 2(9.8 m/s^2)(440m)
v=7.35m/s

now the answer in the book is 5.0m/s and i was wondering what is the mistake that is made ?? or is the book just incorrect?

2. Nov 21, 2009

### kuruman

Start with kinetic + potential at 440 m is equal to kinetic plus potential at 387.2 meters. Use different symbols for the speed v and the height h. Your problem is you plugged the numbers in the wrong places because everything looks the same.

3. Nov 22, 2009

### tamir102

thanks will work on it n message back

4. Nov 24, 2009