A railroad worker realizes that a car on a slope does not have its brakes set and
will roll down. He runs to the car to set the brakes. At t = 0 , when he is at
distance x0 behind the car, it starts to roll, accelerating at constant rate 2 m/s2 .
He is running at constant speed 4 m/s .
What is the largest value of x0 that will allow him to catch the rolling car?