I'm hoping to get some clarification on this. I'd like to see if I did it right, and if not then I'd really like to know what I did wrong.

A car is traveling at 20.83m/s , it takes 3.4s to stop, what is the displacement?

d=1/2(V1+V2)t

= 1/2(20.83m/s+0m/s)(3.4)

= 1/2(70.83)

= 35.42m

It seems right, but in my lesson text they say that formula only applies to situations of constant velocity, and I don't believe this is constant velocity.

I appreciate any help, thanks very much.