1. The problem statement, all variables and given/known data A man (weighing 915 N) stands on a long railroad flatcar (weighing 2805 N) as it rolls at 18.0 m/s in the positive direction of an x axis, with negligible friction. Then the man runs along the flatcar in the negative x direction at 40.00 m/s relative to the flatcar. What is the resulting increase in the speed of the flatcar? 2. Relevant equations Pi = Pf 3. The attempt at a solution (915+2805)g(18)=(915)g(-40+18)+(2805)g(v+18) v=-1.3 m/s But this is the wrong answer...what am I doing wrong???