How to calculate momentum at right angle

[eulerddx4]

Hello,

I am trying to figure out how to calculate the momentum of something at a right angle.

basically a hockey puck is traveling on the x-axis and hits a stationary hockey puck. One of the hockey pucks goes up the y-axis (puck A) and one hockey puck goes down the y-axis (Puck B). Am I supposed to use m*v*sin90 ? and m*v*sin-90 ? or do I use cosine? I'm fine calculating with triangles but I don't know what to do when things (forces, momentums) are at right angles

 

[Simon Bridge]

There has to be something else.

Before the collision you have momentum p in the x dir.
After collision you have no momentum in the x direction.
Therefore, momentum was not conserved in the collision.
Need more information.

Example - conservation of momentum:
If the incoming puck was A, and it finishes with momentum p (same as initial) in the +y dir, then puck B would head off with momentum about (1.4)p at 45 degrees... preserving the zero total momentum in the y dir and the p total momentum in the x dir.