The impulse of a force is defined as the product of average force (F) and the time for which it acts.
Here, the mass of the car is 2000 kg. The impulse of the car is 10000 N*s.
Using the formula for impulse 10000 = 2000*a*t
=> a*t = 5 m/s
The product of acceleration and time is the change in velocity. In this case it is 5 m/s.
It is not possible to determine the time for which the collision lasts from the values that are given. The data given is insufficient to determine how long the collision lasted for.