Motion in one dimension- Find acceleration and original velocity

[Xen]

Homework Statement

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

Homework Equations

a= [v-v_o]/t-t_o

Constant acceleration:
v=v_o + at
x= x_o + v_ot + (1/2)at²

Constant velocity:
x=vt +x_o

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 = V_o + [ (2.8 m/s)² - V_o² / 80 ]* (8.50)

2.8 m/s = V_o + 66.64/80 - (8.50V_o²)/80

 

[Kurdt]

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

 

[Xen]

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

 

[Kurdt]

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