# Emergency help (2 object motion)

1. Oct 11, 2005

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 wont 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 seperation 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 dont 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

2. Oct 15, 2009

### 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.