A park ranger driving on a back country road suddenly sees a deer “frozen in the headlights 20.0 m ahead. The ranger, who is driving at 11.4 m/s, immediately applies the
brakes and slows with an acceleration of magnitude 3.80 m/s. How much distance is
required for the ranger's vehicle to come to rest?
Picture the Problem
We choose the positive x direction to be the direction of motion. With this choice it
follows that the initial velocity is v; = +11.4 m/s. In addition, the fact that the ranger's
vehicle is slowing down means that its acceleration points in the opposite direction to the
velocity. Therefore, the vehicle's acceleration is a = -3.80 m/s2. Finally, when the vehicle
comes to rest, its final velocity is zero, ve = 0.