# 2-d collision problem

1. Nov 2, 2013

### dnawiam

1. The problem statement, all variables and given/known data
A neutron of mass 1.7 X 10^-27 kg travelling at 2.2 km/s, hits a stationary helium nucleus of mass 6.6 X 10^-27 kg. After the collision, the velocity of the helium nucleus is 0.53 km/s at 52° to the original direction of motion of the neutron. Determine the final velocity of the neutron.

2. Relevant equations

pi1x+pi2x=pf1x+pf2x
pi1y+pi2y=pf1y+pf2y

3. The attempt at a solution

I changed all the km/s to m/s since the answer is in m/s

(1.7X10^-27(2200)-6.6X10^-27(530cos52))/1.7X10^-27=vficos∅
933.18m/s=vficos∅

Well, it does not matter what i get for the y component since the answer 1.9 m/s and 933 is just too high.
So, is the answer wrong or did i do something wrong.
1. The problem statement, all variables and given/known data

2. Relevant equations

3. The attempt at a solution

2. Nov 2, 2013

### TSny

I think the answer you were given should have been 1.9 km/s rather than 1.9 m/s.

3. Nov 2, 2013

### dnawiam

Well, I did solve it for km/s I got 1.05 km/s.
vf2y=0.53sin52
vf2y=0.418km/s
vf2x=0.933 km/s

If you use the Pythagorean theorem you get 1.05km/s

4. Nov 3, 2013

### TSny

You did not account for the masses of the particles in this calculation.

5. Nov 3, 2013

### dnawiam

You are right. How silly of me. Well, I got 1.9 km /m for my answer. Thanks for your help.