Conservation of Momentum: Solving a Collision Problem

[Cheesy74]

Homework Statement

If an object with momentum n going right collides with an object with momentum 2n going left, will the right-moving object go left at momentum n while the left-moving object stops, or will both objects move left at momentum n/2?

The Attempt at a Solution

Obviously, the opposing forces are going to cancel out, but I'm not sure if the remaining n momentum is going to be distributed between both objects or not. Could someone give me a quick solution here?

 

[LowlyPion]

Presumably this is an elastic collision.

What else needs to be conserved?