# Elastic Collision, Equal Masses

Okay, i have a problem here with 2 dimensional elastic collision between 2 balls with equal mass, they are both moving in differant directions before collision

what i know:

vx and vy of both balls,
the slope of their movement, which can be converted to an angle with tan-1 x

the problem is all ive got so far is momentum conservation with

m1v1 + m2v2 = m1v1' + m2v2'

but of course we have 2 unknown variables here v1' and v2'

so how do i use slope or angle to get v1 or v2 and then the other is easy to solve for.

thanks

EDIT: could i use impulse (J = Ft) and use a really small number of time and we know that J = p2 - p1

EDIT2: and where could i get the F in impulse from? cant really use newtons second law of F = ma here because then i would need to know the acceleration of what it hit was which is essentially what finding J does for me... so anyone know of a better method??

cruncher

Last edited:

A.T.
Hints:

- treat it as a 1 dimesional problem along the collision axis (connects centers of the balls). nothing changes perpedicular to it

- m1 = m2 in your case

- use the reference frame of one ball for calculation (one initial v becomes zero)