To convert miles per hour to meters per second divide by 2.237
128 miles per hour / 2.237 = 57.22 meters per second.
Using the first equation:
57.22 = sqrt(2 x 9.81 x h)
Remove the sqrt by raising both sides to the second power:
57.22^2 = (2 x 9.81 x h)
Simplify Both sides:
3274.1284 = 19.62h
Divide both sides by 19.62:
H = 3274.1284/ 19.62
H = 166.88 meters