Two cars with an initial clearance of 60ft are traveling 5delta.deltadeltadelta ft/s when car A slows down, decelerating at 5ft/s^2 until 25ft/s and then maintaining that speed.  The driver of car B is talking on the cell phone and thus suffers from Inattentional blindness*.  The driver of car B does not begin braking until the clearance between the cars is 20ft.  How hard must the driver of B then brake to just avoid collision (i.e. what acceleration must car B then have to make the smallest clearance between the cars equal to zero)?  Draw clear a-v-r curves for both vehicles and determine how much time will elapse from when A begins to brake until the near-collision occurs? 

* That's what it's called. Look it up.