Elastic Collisions in One Dimension

[G-reg]

Homework Statement

A cart with mass 310 g moving on a frictionless linear air track at an initial speed of 1.4 m/s undergoes an elastic collision with an initially stationary cart of unknown mass. After the collision, the first cart continues in its original direction at 0.64 m/s.

Homework Equations

(1/2)m1vo^2 +(1/2)m2vo^2 = (1/2)m1vf^2 + (1/2)m2vf^2

The Attempt at a Solution

(310)(1.4)^2 + 0 = (310)(.64)^2 + m2vf^2

(310)(1.4)^2 - (310)(.64)^2 = m2vf^2

but I feel like I need vf to find m2 so how am I supposed to go from here?

 

[ideasrule]

Two things have to be conserved in an elastic collision. One is energy, which you have. What's the other one?

 

[G-reg]

And momentum
which would be

m1v1o = m1v1f + m2v2f ?

 

[roflol]

you sure it didnt say "inelastic" instead? and what exactly are they asking you to work out : /