# 2D momentum collision question

1. Jan 19, 2012

### Meco

1. The problem statement, all variables and given/known data
The drawing shows a collision between two balls. Ball A has a mass of .030kg and is moving along the x axis with a velocity of +5.5 m/s. It makes a collision with ball B, which has a mass of .055kg and is initially at rest. The collision is not head-on. After the collision, the two balls fly apart with the angles shown in the drawing below
What is the final velocity of ball A and B?

... .... | Ball A
... .... | 65°
. A ---B---
... .... | 37°
... .... | Ball B

Can't get above picture to look right, going to take a picture of it and save it in the post

A and B show the start position and Ball A and Ball B shows where they finish
2. Relevant equations
M1V1 + M2V2 = M1V1'+ M2V2'
Using inverse trig?

3. The attempt at a solution
I saw basically the same problem in Khan's academy and in there he had one of the two ball's final velocity given. I have no real idea how to solve for two variables but here was my try:
Momentum in X initial= 5.5 * .03 = .165
Momentum in Y initial= 0
m1v1+ m2v2= m1v1'+ m2v2'
.030*5.5 + 0 = .03v1' +.055v2'

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Last edited: Jan 19, 2012
2. Jan 19, 2012

### Spinnor

You should have three equations,

Energy before = energy after

Momentum in x direction before = momentum in x direction after

Momentum in y direction before = momentum in y direction after

3. Jan 19, 2012

### Meco

Ok, well the energy before and after equation is:
(.03*5.5)+ (0.055*0)= (.03*V1')+(.055*V2')
Momentum in X before:
.030*5.5
Momentum in the Y before:
0
Momentum final for X must equal .165
Momentum final for Y must equal 0
I do not really understand how I can use this to find two velocities without knowing atleast one of them. How do I use the angles given to help me figure this out?

4. Jan 19, 2012

### Spinnor

Write it out, if you see it written out it might click, if not it did not take too much time. I don't think you need the energy equation. You have two unknowns, the magnitudes of the velocity of each mass after collision so you only need two equations in the unknowns.