If a vehicle is moving with a velocity of 20 m/s and comes to a stop after 4 seconds, its final velocity will be 0 m/s.
Velocity is defined as the rate of change of displacement over time. When the vehicle stops, its displacement becomes zero, and since it takes 4 seconds for this change to occur, the final velocity will be zero.
Therefore, the final velocity of the vehicle is 0 m/s.