1. The problem statement, all variables and given/known data A train slows down as it rounds a sharp horizontal turn, slowing from 90 km/h to 50 km/h in the 15 s that it takes to round the bend. The radius of the curve is 150 m. Compute the total acceleration at the moment the train speed reaches 50 km/h 2. Relevant equations a = sqrt[a_t^2 + a_r^2] 3. The attempt at a solution I have the solution for the total acceleration, I'm just wondering what I am supposed to give the angle relative to in these kinds of problems in general. The answer key gives the angle relative to the final velocity vector, is that a good reference point in general?