# 2-d collision problem

## Homework Statement

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.

## Homework Equations

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

## 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.

## The Attempt at a Solution

TSny
Homework Helper
Gold Member
I think the answer you were given should have been 1.9 km/s rather than 1.9 m/s.

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

TSny
Homework Helper
Gold Member
Well, I did solve it for km/s I got 1.05 km/s.
vf2y=0.53sin52
vf2y=0.418km/s

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

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

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