a car is moving at 17.7 m/s when it begins to slow down with a deceleration of 2.5 m/s2. how long does it take to travel 20 meters as it slows down

20 = 17.7t -(1/2)(2.5)t^2

1.25 t^2 - 17.7 t + 20 = 0
solve quadratic for t

t = 1.24 or t = 12.9

well, of course it will get there in 1.24 seconds

then, while we are looking the other way, it keeps deaccelerating until it stops, then comes screaming back at the guy taking pictures at the 20 meter mark. At 12.9 seconds it hits him in the back as he is fiddling with his cell phone. We ignore that second solution.