Posted by Andres on .
A speedboat starts from rest and accelerates at +1.99 m/s2 for 7.00 s. At the end of this time, the boat continues for an additional 6.00 s with an acceleration of +0.515 m/s2. Following this, the boat accelerates at 1.44 m/s2 for 8.00 s. What is the velocity of the boat at t = 21.0 s?

physics 
drwls,
The velocity change during each interval is (acceleration rate)*(time)
Add the velocity changes for the three intervals. The velocity will drop durng the third interval because of deceleration (negative acceleration).