# Involves physics but I have to program, can't figure out equation

1. Oct 21, 2011

### CProgWiz

Involves physics but I have to program, can't figure out equation!!!

1. The problem statement, all variables and given/known data
Imagine an experiment performed on an infinitely long “billiards” table. This table is bounded at the far side and the near side, and these sides are a distance w apart. A ball (of diameter 0) is adjacent to the near side, at x coordinate 0. It is sent off at an initial speed v and at an angle . (is measured as follows: if the ball heads straight to the left, that would be -90 degrees, if it heads straight across that would be 0degrees, and if it heads straight to the right that would be 90 degrees.) The ball decelerates at a rate of d. When the ball bounces off either side, the bounce is “true”; that is, it bounces off just like a ray of light bouncing off a perfect mirror. The collisions with the top or bottom of the table absorbs no energy.

Compute all points where the ball hits the lower wall before it runs out of energy and stops.
(In the x direction)
2. Relevant equations

I don't know, that's what I need help figuring out!

3. The attempt at a solution

Well, I was thinking that the angle at which the ball is struck in the beginning, must be equal to the angle that the ball bounces off the wall at, each time.

I'm not sure if I should use momentum, or what! I'm more or less LOST! Help please.

2. Oct 22, 2011

### Staff: Mentor

Re: Involves physics but I have to program, can't figure out equation!!!

An often used trick for theses sorts of problems is to imagine stacking a series of mirror-image versions of the table side by side or end to end. Then imagine that the ball, when it strikes a side, rather than bouncing it passes through to the next mirror-image table and proceeds in a straight line. This straight line motion image simplifies things considerably since you can use a single equation for a line for the path.

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