# Looking for verification on a momentum & collision problem

1. Jun 13, 2006

### PHYclueless

Here is the problem:
Runner1 is going 20 degrees NofE with a mass of 60kg and v=5m/s. Runner2 is going 20 degrees NofW with a mass of 80kg and v=4m/s when they collide. What are their respective momentums prior to the collision? What is their final velocity and direction after collision if it was perfectly inelastic collision?

For question1 I got L=300kgm/s for runner1 and L=-320kgm/s for runner2.

For question2 I'm a little perplexed. This is what I did.
(x) m1v1+m2v2=(m1+m2)vf
-4sin20(80kg)+5sin20(60kg)=(60kg+80kg)vf
-109+103=140vf
-6=140vfx
vf(x)=-.049m/s

(y) m1v1+m2v2=(m1+m2)vf
4cos20(80kg)+5cos20(60kg)=(60kg+80kg)vf
301+282=140vf
583=140vf
vf(y)=4.16m/s

Then I took the TAN-1(4.16/-.049) to find theta and it gave me -89degrees North of East.

Does this look right?

Thank you to anyone who can give me some insight. I appreciate your help.

2. Jun 14, 2006

### arunbg

Your method is right.
But your vector algebra is slightly flawed.
For (x) take cosine and not sine.
Viceversa for (y) .