Conservation of Motion Collision of two object

[kbward]

Homework Statement

A small car is moving at 1.3 m/s on an air track when it collides with a larger 3 kg cart at rest. After the collision, the small cart recoils at 0.850 m/s.
What is the speed of the large cart after the collision?

Homework Equations

m₁V_1i + m₂V_2i = (m₁+m₂)V_2f

m₁ = .2 kg
m₂ = 3 kg
V_1i = 1.3 m/s
V_2i = 0
V_1f = -.85 /ms
V_2f = ?

The Attempt at a Solution

.2*1.3 + 3*0= (.2+3) V_2f
.26 = 3.2 V_2f
V_2f = .26/3.2
V_2f = .08125

My answer came back wrong. Where am I making a mistake?
Thanks

 

[radou]

If this is an elastic collision, then the carts don't move together after the collision.