Need help with simple acceleration problems.

[ksaechao]

Here's one:

Craig got up to 133.5 km/h getting around a slower vehicle within the length of the passing lane. He then spotted a police cruiser coming around the corner and hit the brakes, slowing to 100 km/h in 0.9 seconds. How much distance did he travel in this time

So I'm pretty much confused with acceleration problems and identifying intial velocity and final velocity. I kow that t=.9 secs. So is the initial velocity 133.5 km/h and final velocity is 100 km/h?

Would I first use the delta s=vi(t)+ 1/2(a)t^2 equation to find the displacement of when he slowed down?

 

[mjsd]

Here's one:

Craig got up to 133.5 km/h getting around a slower vehicle within the length of the passing lane. He then spotted a police cruiser coming around the corner and hit the brakes, slowing to 100 km/h in 0.9 seconds. How much distance did he travel in this time

So I'm pretty much confused with acceleration problems and identifying intial velocity and final velocity. I kow that t=.9 secs. So is the initial velocity 133.5 km/h and final velocity is 100 km/h?

yes.

Would I first use the delta s=vi(t)+ 1/2(a)t^2 equation to find the displacement of when he slowed down?

to use this you need to assume that acceleration is constant. at this stage you have only 3 known variables: u, v and t. but from these you can work out the average (de)acceleration