Applications of the Equations of Kinematics for Constant Acceleration

[jacksonpeeble]

Homework Statement

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.

Homework Equations

http://www.webassign.net/ebooks/cj6/pc/c02/read/main/c02x2_4.htm
(Hopefully this is public access, if not, the equations can be determined from the work below, assuming that I am using the correct equations.)

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!

 

[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.

 

[jacksonpeeble]

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.

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..."?