Two objects colliding & sticking together, what is their final speed?

[itsmarasilly]

Homework Statement

Two freight cars, each with a mass of 2.5 multiplied by 10^5 kg, collide and stick together.
One was initially moving at 3.4 m/s and the other was at rest. What is their final speed?

Homework Equations

m(vf-vi)

The Attempt at a Solution

(2.5*10^5)(0-3.4)= -850,000
= -8.5 * 10^5 m/s

 

[vineroon]

The main thing you can use in the problem is conservation of momentum:

m₁v₁+m₂v₂=(m₁+m₂)v'

This equality is a result of the completely inelastic collision. The question asks you to solve for v'.