A ball is dropped from a height h off the ground. After each bounce, the ball returns to a height of two thirds of the height of the previous bounce . What is the total distance travelled by the ball? Assume it moves only in the vertical plane and that it continues bouncing indefinitely.
This section requires Javascript.
You are seeing this because something didn't load right. We suggest you, (a) try
refreshing the page, (b) enabling javascript if it is disabled on your browser and,
finally, (c)
loading the
non-javascript version of this page
. We're sorry about the hassle.
Each bounce is two thirds of previous height:
h n = 3 2 h n − 1
Total distance is the original height plus twice the height of each bounce:
d = h + 2 ∑ n = 1 ∞ ( 3 2 ) n h
Simplifying:
d = h + 2 h ∑ n = 1 ∞ ( 3 2 ) n
Sum to infinity:
S ∞ = 1 − r a where a = 3 2 , r = 3 2
S ∞ = 3 2 ÷ ( 1 − 3 2 ) = 3 2 ÷ 3 1 = 2
Therefore:
d = h + 2 h × 2 = h + 4 h = 5 h