Finding Final Velocity in a Spring Loaded Collision

[pleasehelpme6]

Spring Loaded Collision, help!

[PLAIN]https://wug-s.physics.uiuc.edu/cgi/courses/shell/common/showme.pl?cc/DuPage/phys2111/summer/homework/Ch-09-10/IE_spring_loaded_collision/springloadedcollision.gif

Homework Statement

A cart with mass m1 = 3.2 kg and initial velocity of v1,i = 2.1 m/s collides with another cart of mass M2 = 4.3 kg which is initially at rest in the lab frame. The collision is completely elastic, and the wheels on the carts can be treated as massless and frictionless. What is the velocity of m1 after the collision in a coordinate system where the center of mass of the two carts is not moving (the "center of mass frame") ?

Homework Equations

p = mv
m1v1 = m2v2

The Attempt at a Solution

i used m1 = 3.2
m2 = 3.2+4.3
v1 = 2.1
v2 = v

so i had, (3.2)(2.1) = (3.2+4.3)v
when i solved for v i got 0.896, but this isn't right, so i don't know what its asking for.

 

[pleasehelpme6]

i guess what i need to know is how to find the velocity of the center of mass

 

[pleasehelpme6]

nevermind, i solved it.

velocity of center of mass was the value i got before (0.896). to solve for the final velocity of m1, i had to do vi - vcm (2.1 - 0.896).

Thanks anyway!