- #1
Pual Black
- 92
- 1
Homework Statement
hello
i have a question to this solved problem in the book
" Mathematical Methods for Physics and Engineering Third Edition K. F. RILEY, M. P. HOBSON and S.J. BENCE "
page 118
Consider a ball that drops from a height of 27 m and on each bounce retains only a third
of its kinetic energy; thus after one bounce it will return to a height of 9 m, after two
bounces to 3 m, and so on. Find the total distance traveled between the first bounce and
the Mth bounce.
Homework Equations
i have to use this equation
[tex]S_M=a \frac{1-r^M}{1-r}[/tex]
so [tex]a=9[/tex] because he wants the distance from the first bounce
if he just said " find the total distance " i have to put a=27 right?
the common ration is [tex]d=\frac{1}{3}[/tex]
the ball goes up and down so i have to multiply the sum by 2 to get the total distance
now
[tex]S_M=2*9 [\frac{1-(\frac{1}{3})^{M-1}}{1-\frac{1}{3}}][/tex]
[tex]S_M=27 [1-(\frac{1}{3})^{M-1}][/tex]
i only don't understand why he put (M-1) not just (M)
The Attempt at a Solution
i thought maybe if I just put M then the ball will bounce for last time and be hanging in the air.
but if i put M-1 then the ball will hit the ground and stop
right?