The arrows in the figure represent the linear momentum of two balls before they collide. If the collision is perfectly inelastic, find the linear momentum after the collision. If the collision is perfectly elastic, find the linear momentum after the collision.
(Ignore whatever is written in pencil)
I've been trying to solve this problem, but I'm not sure what should I do, or where should I start. I asked my teacher if I had to take into account angles (which are not given), and she just said no. I honestly don't know what to do, can you help me out?