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## Homework Statement

The setup is there are two pucks (m

_{1,}m

_{2}) on an air table and they undergo elastic collision while m

_{2}is stationary. I am asked to find the angle between the two velocities but I can't figure out how without being giving at least one angle.

Variables:

m

_{1}= 28.0 g = 0.28 kg

m

_{2}= 102 g = 0.102 kg

v

_{1}= 0.785 m/s

v

_{2}= ?

## Homework Equations

K

_{i}= (1/2)m

_{1}v

_{1i}

^{2}

K

_{f}= K

_{i}

K

_{f}= (1/2)m

_{1}v

_{1f}

^{2}+ (1/2)m

_{2}v

_{2f}

^{2}= K

_{i}

## The Attempt at a Solution

First I went about finding what v

_{2}was by using K

_{f}= K

_{i}

(1/2)(0.028)(0.785)

^{2}+ (1/2)(0.102)v

_{2f}

^{2}= (1/2)(0.028)(1)

^{2}

(0.008) + (1/2)(0.102)v

_{2f}

^{2}= (0.014)

v

_{2f}

^{2}= (0.117)

v

_{2f}= 0.343 m/s

Now this is the part I'm stuck, since they want me to find the angle between v

_{1}and v

_{2}. If they had given me at least an angle for m

_{1}I could use [0 = m

_{1}v

_{1f}sin[tex]\theta[/tex] - m

_{2}v

_{2f}sin[tex]\theta[/tex]] but I have no angles to work with, and I'm not sure how I should arrange the equations to find the angle. If I were to guess I would say that they angle would be 90

^{o}since m

_{2}was stationary, but I'm not sure how to prove that and I don't think it applies to this case since I have two different masses.

If anyone could help me understand this problem, that would be great!