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?

Answer 1

V = a1*t1 + a2*t2 -a3*t3,
V = 1.99 * 7.0 + 0.515 * 6 - 1.44 * 8 = 13.93 + 3.09 - 11.52 = 5.5 m/s.