# Homework Help: Collision in two dimensions (not heads on)

1. Jun 14, 2009

### salim271

1. The problem statement, all variables and given/known data
Puck A has a mass of 0.0320 kg and is moving along the x axis with a velocity of +7.65 m/s. It makes a collision with puck B, which has a mass of 0.0640 kg and is initially at rest. The collision is not head-on. After the collision, the two pucks fly apart with the angles 65 and 37 respectively for A and B, Find the speed of (a) puck A and (b) puck B.

2. Relevant equations
m1v1 + m2v2 (final) = m1v1 + m2v2 (initial) <--- Must be broken down into components x and y since two dimensions...

3. The attempt at a solution
Mass of A: .0320 kg
Magnitude Velocity (initial) of A (Vo): 7.65 m/s
Mass B: .0640 kg
Magnitude Velocity (initial) of B (Vo2): 0 m/s

I didn't get really far...

(x component) (.0320 kg)(7.65) + 0 = (.0320)(vf) + (.0640)(vf2)

(y component) 0 = (.0320)(vf) + (-0.640)(vf2)

I'm not really sure where to go from here... my homework suggested solving for a variable in y and substituting it in for x, but if i solved for say, vfy and tried to substitute it in, the variable would be vfy, not vfx, so wouldnt it not substitute?? I really need a good explanation for this because my teacher didn't cover it well in my opinion, he gave an example of one problem and didn't finish it, claiming the rest we could solve on our own because it was solving for two variables which we should have learned in math, but i cant remember how... any help would be great i really need it!
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Jun 14, 2009

### turin

Are you comfortable with trigonometry? The problem gives you the angles (although they are a bit ambiguous). Those angles basically give you the relationships between the x and y components.

3. Jun 14, 2009

### salim271

I'll admit its been awhile since I've been deep in trig, I don't remember enough to see the relationship the angles play to understand how to solve a problem like this...

4. Jun 15, 2009

### ideasrule

Consider an object moving at 100 m/s "a" degrees from the horizontal. Draw a diagram or imagine the situation in your head. That object's speed in the x direction would be 100cos(a); its speed in the y direction would be 100sin(a). Does that clear things up a bit?