# Homework Help: Motion in one dimension- Find acceleration and original velocity

1. Sep 11, 2008

### Xen

1. The problem statement, all variables and given/known data
A truck covers 40.0m in 8.50s while smoothly slowing down to a final velocity of 2.8 m/s. a) Find the truck's original speed b) Find its acceleration

2. Relevant equations
a= [v-vo]/t-to

Constant acceleration:
v=vo + at
x= xo + vot + (1/2)at2

Constant velocity:
x=vt +xo

3. The attempt at a solution

well i've made pages of attempts in my notebook...but here's a sample of what i've tried

2.8 m/s = Vo + [ (2.8 m/s)2 - Vo2 / 80 ]* (8.50)

2.8 m/s = Vo + 66.64/80 - (8.50Vo2)/80

2. Sep 11, 2008

### Kurdt

Staff Emeritus
You have a quadratic equation in the initial speed. How would you solve a quadratic equation.

3. Sep 11, 2008

### Xen

Set it equal to zero then use the quadratic formula which would give the initial speed?

4. Sep 11, 2008

### Kurdt

Staff Emeritus
Yes, that is how you would solve for the initial velocity.