A Train starts from rest and speeds up for 15 min until it reaches a constant velocity of 100 mph. It stays at this speed for half an hour. Then it slows down for another 15 min until it is still. Which statement correctly describes the position vs. time graph of the train's journey?
A) The first 15 min is a curve that is concave upward, the middle portion is a straight line with slope 100 mph, and the last portion is a concave downward curve.
OR
B) The first 15 min is a curve that is concave downward, the middle portion is a straight line with slope 100 mph, and the last portion is a concave upward curve.?