Find deceleration, given initial velocity and final distance

[EricPowell]

Homework Statement

A car traveling at 88ft/s skids 176ft after its brakes are applied. The deceleration provided by the braking system is constant. What is its value?

The Attempt at a Solution

$$
v_0=88 \\
v_f=0 \\
d_0=0 \\
d_f=176
$$
$$
d(t)=\int88\,dt \\
d(t)=88t+c \\
0=88(0)+C \\
C=0 \\
176=88t \\
t=2s
$$
$$
a=\frac{Δv}{Δt} \\
=\frac{-88}{2} \\
=-44ft/s
$$
The answer key of the textbook says that the deceleration is -22ft/s². :(

 

[milesyoung]

You have assumed motion with constant velocity in finding d(t). You need to use the kinematic relationships that deal with motion with constant acceleration:
http://hyperphysics.phy-astr.gsu.edu/hbase/acons.html

Those should give you 2 equations in 2 unknowns.