Thank you for the welcome.
Okay so an elastic collision means that K is conserved throughout the collision.
Therefore:
(.5)m1v1i2 = (.5)m1v1f2 + (.5)m2v2f2
But that leaves me in the same situation as before doesn't it?
Homework Statement
A cart with mass 340 g moving on a frictionless linear air track at an initial speed of 1.2 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 0.66 m/s.
(a) What is...