I was given the mass and velocity of an object, and I know that it is traveling in a straight line along the x-axis (so I suppose I've been given a second angle). It collides with an object with known mass at rest. The first object rebounds at a given angle. What is the velocity (magnitude and direction) of the second object after the collision? You can't assume that it's an elastic collision.
I started with two component forms of the conservation of momentum equation, and reduced to three variables by replacing $Ax'$ with $A'cos(\theta A')$, and so on for each component. But now I have three variables and two equations! I've racked my brain, and I can't think of what to use as a third equation. What should I do?