Two trains heading straight for each other on the same track are 250 m apart when their engineers see each other and hit the brakes. The A, heading west at 96 km/h, slows down, accelerating at an average of -4 m/s^2, while the B, traveling at 110 km/h, slows down, accelerating at an average of -3 m/s^2. Will they collide? I solved it this way : a_T = The resultant of two accelerations = -7 V_A = 96 km/h V_B = 110 km/h V_T = V_B + V_A = 206 km/h = 57.22 m/s And considered (V_T)_final = 0. Plugging into this formula : S = - [(V_T)^2 ] / 2 a_T; S = 233.9. So two trains won't collide. My answer for S is not the same as the one in the solutions manual, 244.5 m. Why is my answer 233.9 ? The book has solved that problem in a different way, and I can do it so, but I'm interested to know why my answer is wrong.