How would you figure out this General Physics problem?

The driver of a truck slams on the brakes when he sees a tree blocking the road. The truck slows down uniformly with acceleration -6.1 m/s2 for 4.20 s, making skid marks 64.4 m long that end at the tree. With what speed does the truck then strike the tree?How would you figure out this General Physics problem?
We first want to find the initial velocity of the truck. Use:





x = 1/2 * a * t^2 + v0 * t + x0





We know the track travels a distance of 64.4 m in 4.20 s while decelerating at -6.1 m/s^2. So we have the following info:





a = -6.1 m/s^2


x = 64 m


t = 4.20 s


x0 = 0





Plug these in and solve for v0. I get v0 = 28.14 m/s





Now we use this to find the final velocity of the truck.


Use the equation:





v1 ^ 2 = v0^2 + 2ax





We know:


v0 = 28.14 m/s


a = -6.1 m/s^2


x = 64.4 m





Now calculate v1. I get v1 = 2.49 m/s.





So the truck is traveling at a speed of 2.49 m/s when it strikes the tree.





Hope this helps.