Help in undrstanding this solution

[transgalactic]

i got a ball with insignificant mass which is being thrown in angle beta
from the top of a slope
how much times this ball will bounce on this slope??

i understand the solution till some point
from which i don't understand what are they doing?

http://img376.imageshack.us/img376/745/28160523vc9.gif

 

[Avodyne]

When the ball bounces, the x component of its velocity is unchanged, and the y component changes sign (from negative to positive). Then, with these initial conditions, it just follows the usual parabolic trajectory until the next bounce.

 

[transgalactic]

so by your words i can understand that their X axes is parralel to the slope
and the y axex is perpandicular to it.

in that case y cannot be negative.

first the constructed equations for the flight in X axes and Y axes
and the calculated the time which took the object from the lift of
to the landing.

after that they give a weird absolute value equations
why??

 

[nrqed]

i got a ball with insignificant mass which is being thrown in angle beta
from the top of a slope
how much times this ball will bounce on this slope??

i understand the solution till some point
from which i don't understand what are they doing?

http://img376.imageshack.us/img376/745/28160523vc9.gif

The solution does not make sense to me. Where did you get it from? They seem to assume that the value of Vy at each bounce is the same but that does not make sense since the force of gravity will accelerate the particle.