Homework Help: 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.