Finding velocity of elastic collision with angles

[Valenti]

Homework Statement

A red ball and blue ball are sliding on a frictionless surface, each ball has a mass of 40g. They collide in an elastic collision. Initially the red one is at rest and the blue one is traveling in the x direction with a speed of 4 m/s. After the collision the blue one is traveling in the direction +35 degrees, with the red one traveling in the direction ‐55 degrees. Using conservation of energy and momentum find the speed of each puck after the collision

Homework Equations

Conservation of momentum: M₁V_i1+ M₂V_i2 = M₁V_f1 + M₂V_f2
Conservation of kinetic energy: 1/2MV_i1² + 1/2MV_i2² = 1/2MV_f1² + 1/2MV_f2²

The Attempt at a Solution

Started using conservation of kinetic energy and got 4 = V_f1 + V_f2
Wasn't sure how to isolate V plugged it into Conservation of momentum factored out m setting V_f1 + V_f2 to 4
0.04kg(4m/s)+ 0 = 0.04kg (4)
It didn't seem to do anything and I'm not exactly sure where I'm supposed to use the angles

 

[Herman Trivilino]

Started using conservation of kinetic energy and got 4 = V_f1 + V_f2

Good start.

To use the conservation of momentum equation you have take into account that it's a vector equation. Which means it's really two equations. One in the x-direction, one in the y-direction. That's where those angles will enter.