# Homework Help: Applications of the Equations of Kinematics for Constant Acceleration

1. Sep 24, 2009

### jacksonpeeble

1. The problem statement, all variables and given/known data
A speedboat starts from rest and accelerates at +2.01 m/s2 for 6.55 s. At the end of this time, the boat continues for an additional 6.45 s with an acceleration of +0.518 m/s2. Following this, the boat accelerates at -1.49 m/s2 for 8.80 s.

Find the total displacement of the boat.

2. Relevant equations
(Hopefully this is public access, if not, the equations can be determined from the work below, assuming that I am using the correct equations.)

3. The attempt at a solution
v0=0
d1=0*6.55+.5*2.01*6.55^2=43.117
v1=2.01*6.55+.518*6.45=16.5066
d2=16.5066*6.45+.518*6.45^2=128.018
v2=16.5066+-1.49*8.8=3.3946
d3=3.3946*8.8+-1.49*8.8^2=-85.5131

Any help is, as always, greatly appreciated! Thank you in advance!

2. Sep 24, 2009

### Delphi51

I agree with your first distance (43.117) after time 6.55 s.
However, at this time I get
velocity = Vi*t + .5*a*t^2
= 0 + .5*2.01*6.55^2 = 13.1655 m/s
This is the initial velocity for the second interval, not 16.5066.

3. Sep 25, 2009

### jacksonpeeble

I see that you changed 6.45 to 6.55. Is this correct, since the problem states "...the boat continues for an additional 6.45 s..."?