physics
posted by Mark .
A ball is dropped from 1.5m and bounces back up 1.2m. How many times will the ball bounce before it loses 90% of its energy? I figued since the ball bouced .8 times the original hight and 10% of 1.5m is .15m that that when the bounce hight reached.15m that 90% of the energy (hight *gravity) was lost. Istarted with 1.5m times .8, then the result * .8 , and so on. 10 times results in a bounce hight of .16. Is this a correct approach?

.8^n = .1
n ln .8 = ln .1
n = 10.31