Halliday, Resnick & Walker — Motion Along a Straight Line: Problem 42

42 You are arguing over a cell phone while trailing an unmarked police car by 25 m; both your car and the police car are traveling at 120 km/hr. Your argument diverts your attention from the police car for 2.0 s (long enough for you to look at the phone and yell, 'I won't do that!'). At the beginning of that 2.0 s, the police officer begins braking suddenly at 5.0 m/s\(^2\). (a) What is the separation between the two cars when your attention finally returns? Suppose that you take another 0.40 s to realize your danger and begin braking. (b) If you too brake at 5.0 m/s\(^2\), what is your speed when you hit the police car?