A driver is arguing over his/her cell phone while trailing an unmarked police ca

Question

A driver is arguing over his/her cell phone while trailing an unmarked police car by 39 m. Both cars are traveling at 29 m/s. The argument diverts the driver's attention from the police car for 2.5 s. At the beginning of the 2.5 s, the police officer begins emergency braking at 5.0 m/s^2. What is the separation between the two cars when the driver's attention finally returns? Suppose that it takes another 0.40 s for the driver to realize the danger and begin braking. If the car also brakes at 5.0 m/s^2, what is the speed of the car when it hits the police car?

Explanation / Answer

at t=0 relative velocity between two cars =0
distance cover by police officer= 1/2*a*t^2=0.5*5*2.5*2.5=15.625m
a)distance between two cars at t=2.5s= 39-15.62=23.37 m
b)vf=vi+at=29-5*2.9=14.5 m/s

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