Physics 1 (college)
posted by Anonymous .
Chap. 7, #36. (II) A ball is dropped from a height of 1.50 m and rebounds to a height of 1.20 m. Approximately how many rebounds will the ball make before losing 90% of its energy?

energy retained each bounce: 1.2/1.4=6/7
(6/7)^n=.1
log of each side
n log (6/7)= 1
solve for n. 
change that fraction to 1.2/1.5 or 4/5. I misread.

I don't understand where you got .1 and then 1 from. Can you explain that?