Acar is travelling at constant velocity. its brakes are then applied, causing uniform

First, note that all these graphs are velocity vs distance graphs. 
Therefore, you need to find a relation that explains how velocity changes with distance.

In a uniformly decelerated motion we have:
s = v₀·t - 1/2·a·t²
v = v₀ - a·t

Solve the first equation for t:
t = [v₀ +/- √(v₀²-2·a·s)] / a
For our purpose what is most important is the dependace:
t ∝ √-s

Now, substitute in the second equation, and we get:
v ∝ √-s

Hence, the graph representing a radical function of a negative value is A).

The final velocity of the object is 16m\s.
Hope this helps! :)