Homework Help: 2D Elastic Collisions

1. Jan 7, 2014

poolec4

1. The problem statement, all variables and given/known data

A 1.0-kg particle is moving in the +x direction at 4.0m/s when it collides elastically with a 4.0-kg particle moving in the −x direction at 1.0m/s After colliding the 1-kg particle moves oﬀ at 130 counterclockwise from the positive x-axis. Find the final speeds of both particles and the direction of the more massive one.

2. Relevant equations

m1*v1=(m1*v3*cos(ø3))+(m2*v4*cos(ø4))

0=(m2*v4*sinø4)-(m1*v3*sin(ø3))

m1*v1^2 = (m1*(v3)^2) + (m2*(v4)^2)

3. The attempt at a solution

(1 kg)(4i m/s) + (4 kg)(-1i m/s) = 0 ==> The total momentum=0

Is there some sort of trick that can be used for 2 dimensional elastic collisions when the masses and speeds swap? Also, since the total momentum is 0, can it be specified as a center-of-mass system, thus being able to use the scattering angle? Thanks in advance for any help!

2. Jan 7, 2014

TSny

Hello poolec4. Welcome to PF!

What is the total momentum vector after the collision?

What does that tell you about the magnitudes and the relative directions of the individual final momenta?