1. The problem statement, all variables and given/known data A railroad car of mass 12,000 kg collides and couples with a second car of mass 18,000 kg that is initially at rest. After the collision, both move at a speed of 4.8 m/s. What is the initial momentum and initial speed of the first car? 2. Relevant equations The formulas that I´ve used are: Pi = pf = mv vi = pf/m 3. The attempt at a solution So, I´d like someone to confirm my answers: For Pi (initial momentum) I did: Pi = pf = mv = (12,000kg + 18,000kg)(4.8m/s) = 144,000kg.m/s For Vi (initial speed) = Pf/m = 144,000/12,000 = 12m/s. Are my answers correct?