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?
The Attempt at a Solution
Well this is the wrong answer and I have no clue why. I know that the fact that the weights are given and not mass is not an issue since W=ma and a would cancel out on both sides so I cannot figure out why this answer is wrong. Anything else that I can try?