# Energy problem with inelastic collision

1. Jun 11, 2010

### mickellowery

1. The problem statement, all variables and given/known data
A railroad car with a mass 2.50x10^4 kg moves at 4.00 m/s. It collides and connects to 3 more cars each with the same weight as the first, they're moving 2.00 m/s. After they connect the final velocity was 2.50 m/s. How much energy is transformed into internal energy in the collision?

2. Relevant equations
I was trying to use $$\Delta$$E=$$\Delta$$K+$$\Delta$$U=-fkd. I wasn't sure if this was the right approach, and I think maybe I'm setting everything up wrong because I'm not coming up with the right answer.

3. The attempt at a solution

2. Jun 11, 2010

### rock.freak667

The change in kinetic energy should give the work done which should be the same as the change in internal energy.