Accleration problem - car strikes a tree

[Frosty8]

Homework Statement

A car traveling at 25m/s strikes a tree. The front end of the car compresses and the driver comes to rest after traveling 0.72 m. What was the average acceleration of the driver during the collision? Express the answer in terms of "g's," where 1.00g = 9.80 m/s2

Homework Equations

velocity final^2 = velocity initial^2 + 2acceleration(change in distance)

The Attempt at a Solution

velocity final^2 = velocity initial^2 + 2acceleration(change in distance)
o^2=25^2+2a(.72)
so for the acceleration i got -15ms^2/9.8ms^2= -1.53ms^2 and this was wrong. what did i do wrong?

 

[PhanthomJay]

Welcome, Frosty8, to the Physics Forums!

Homework Statement

A car traveling at 25m/s strikes a tree. The front end of the car compresses and the driver comes to rest after traveling 0.72 m. What was the average acceleration of the driver during the collision? Express the answer in terms of "g's," where 1.00g = 9.80 m/s2

Homework Equations

velocity final^2 = velocity initial^2 + 2acceleration(change in distance)

The Attempt at a Solution

velocity final^2 = velocity initial^2 + 2acceleration(change in distance)
o^2=25^2+2a(.72)

yes, correct

so for the acceleration i got -15ms^2/9.8ms^2= -1.53ms^2 and this was wrong. what did i do wrong?

math error: 625 = -1.44a, theerfore, a = -434 m/s^2 , which is how many 'g's'?

 

[Frosty8]

Thank you