Car collision: separation during distracted driving and impact speed

[themadperseid]

Ok, here is the prob.

You are arguing over a cell phone while trailing an unmarked police cruiser by 25m; both you and the cruiser are traveling at 110km/h. Your argument diverts your attention from the police cruiser for 2.0s (long enough to look at the phone and yell "I won't do that!"). At the beginning of the 2.0 s, the cop begins emergency braking at 5.0 m/s^2. (a) What is the separation between the two cars when your attention finally returns, assuming it takes you another .4s to realize the danger and start braking. (b) If you too brake at 5.0 m/s^2, what is your speed when you hit the cruiser.

We have part a as 15, but don't get part b. I represent bout 1/2 of a class, all lost. Please help. We know the end answer is 26.7 m/s

Thanks,
Chris

 

[zack_21]

Write down what you know. You know the change in time, as well as the initial velocity. To find the distance, you need to know how far the cop travels in that much time, and for the final answer you need to find the final velocity of your car.