Answer:
a. After the first bounce, the ball will be at 85% of 8 ft. After 2 bounces, it'll be at 85% of 85% of 8 feet. After 3 bounces, it'll be at (85% of) (85% of) (85% of 8 feet). You can see where this is going. After n bounces the ball will be at
[tex]h(n) = (85\%)^n 6ft = (\frac{17}{20})^n(6ft\times 12\frac{in}{ft}) = (\frac{17}{20})^n\times72'[/tex]
b. After 8 bounces we can apply the previous formula with n = 8 to get
[tex]h(8)=(\frac{17}{20})^8\times 72' = 19.62'[/tex]
c. The solution to this point requires using exponential and logarithm equations; a more basic way would be trial and error using the previous [tex]h(n)[/tex]increasing the value of n until we find a good value. I recommend using a spreadsheet for that; the condition will lead to the following inequality:
[tex]1>(\frac{17}{20})^n\times 72[/tex] Let's first isolate the fraction by dividing by 72.
[tex](\frac{17}{20})^n<\frac1{72}[/tex] Now, to get numbers we can plug in a calculator, let's take the natural logarithm of both sides:
[tex]ln ((\frac{17}{20})^n) < ln \frac 1{72} \rightarrow n\times ln (\frac{17}{20}) < -ln72[/tex]. Now the two quantities are known - or easy to get with any calculator, replacing them and solving for n we get:
[tex]-(0.16)n < - 4.27 \rightarrow n>26.31[/tex] Now, since n is an integer - you can't have a fraction of a bounce after all, you pick the integer right after that, or n>27.
