SOLUTION: A Super Happy Fun Ball is dropped from a height of 8 feet and rebounds 12/13 of the distance from which it fell. How many times will it bounce before its rebound is less than 1

Algebra ->  Sequences-and-series -> SOLUTION: A Super Happy Fun Ball is dropped from a height of 8 feet and rebounds 12/13 of the distance from which it fell. How many times will it bounce before its rebound is less than 1      Log On


   



Question 978610: A Super Happy Fun Ball is dropped from a height of 8 feet and rebounds 12/13 of the distance from which it fell.
How many times will it bounce before its rebound is less than 1 foot?

How far will the ball travel before it comes to rest on the ground?

Answer by Edwin McCravy(20055) About Me  (Show Source):
You can put this solution on YOUR website!
Bounce Number         Rebound
      1          %2812%2F13%29%2A8+=+96%2F13
      2          %2812%2F13%29%2A%2896%2F13%29+=+1152%2F126
      .
      .
      .
      n           a%2Ar%5E%28n-1%29+=+%2896%2F13%29%2812%2F13%29%5E%28n-1%29

We set the nth bounce < 1

%2896%2F13%29%2812%2F13%29%5E%28n-1%29%22%22%3C%22%221

Multiply both sides by 13%2F96

%2812%2F13%29%5E%28n-1%29%22%22%3C%22%2213%2F96

Take logs of both sides:

log%28%28%2812%2F13%29%5E%28n-1%29%29%29%22%22%3C%22%22log%28%2813%2F96%29%29

%28n-1%29log%28%2812%2F13%29%29%22%22%3C%22%22log%28%2813%2F96%29%29

Divide both sides by log%28%2812%2F13%29%29

However since log%28%2812%2F13%29%29=-.0347621063

we are dividing an inequality through by a negative number
and that will reverse the inequality from < to >:


n-1%22%22%3E%22%22log%28%2813%2F96%29%29%2Flog%28%2812%2F13%29%29

n-1%22%22%3E%22%2224.97915041

n%22%22%3E%22%2225.97915041

So the 26th rebound will be the first one less than 1 foot.

How far will the ball travel before it comes to rest on the ground? 

--------------------------------------

Theoretically it will never stop bouncing, but that's theoretically,
not actually.

However we treat it as an infinite series.

The first 8 feet that it fell must be added in separately.

It rebounded 96/13 feet and then fell 96/13 before it hit the ground
the second time.  So the first term is 2×(96/13) = 192/13 and the common
ratio is 12/13



To that we must add the 8 feet it fell in the beginning:

Answer: 192+8 = 200 feet.

Edwin