My problem states: A speedboat starts from rest and accelerates at +2.01 m/s^2 for 7.25s. At the end of this time, the boat continues for an additional 6.05s with an acceleration of +0.518 m/s^2. Following this, the boat accelerates at -1.49 m/s^2 for 8.05s. (a) What is the velocity of the boat at t = 21.35s? (b) Find the total displacement of the boat. So here was my thinking. The boat was speeding up during the first two stages and slowing down during the third. t = 21.35s is nothing more than the three time intervals given in the question added together. So couldn't I just find the velocity for each time interval and then add them together? At least that's what I tried to do, and my answer was incorrect. I was having trouble discerning what the starting velocity would be for the last two intervals as the first one is clearly 0m/s. I'm assuming also that once I've found the velocity at t = 21.35s. I will be able to use that to find the total displacement.