Impulse or the change in momentum is defined as P = F*t, where F is the net average force and t is the time for which the force F acts. For the same impulse, either a small force acts over a long duration of time or a larger force acts over a smaller duration of time.
In the question, a 2,000-kg car collides with a tree and is brought to rest in 0.50 seconds by an average force of 60,000 newtons.
Here, the net average force is 60 kN, and this force acts for a time period of 0.5 seconds.
The magnitude of the impulse on the car is equal to 60,000*0.5 = 30,000 Ns.