# Homework Help: Elastic collision in 2-D?

1. Mar 23, 2009

### Kitty808

1. The problem statement, all variables and given/known data
A hockey puck B rests on a smooth surface of ice and is struck by a second puck A , which was originally traveling at 40.0 m/s and which is deflected 30.0 degrees from its original direction. Puck B acquires a velocity at a 45.0 degree angle to the original direction of A. The pucks have the same mass.
-Compute the speed of puck A after the collision.
-Compute the speed of puck B after the collision.
-What fraction of the original kinetic energy of puck A dissipates during the collision?

2. Relevant equations

3. The attempt at a solution
This has got me really confused. I don't even know where to begin. I drew a diagram thought I was supposed to find the x and y components of A to get the final velocity of A and then change in A equals the negative change in B, but I'm not getting it. Please help!!

2. Mar 23, 2009

### robphy

what diagram did you draw?
what equations would you need to satisfy?

3. Mar 23, 2009

### Kitty808

My diagram shows puck A moving in the positive x direction at 40 m/s and colliding with puck B. After the collision puck A is deflected 30.0 degrees relative to the positive x axis at some final velocity. Puck B moves from rest to some final velocity 45 degrees relative to the negative x axis.
I'm not exactly sure which equation(s) I need. I'm assume because the masses are unknown but equal, the equation change in velocity of A is equal to the negative change in the velocity of B.

4. Mar 23, 2009

### robphy

In general, what happens in a collision?