The initial momentum of the car is
(mass) x (speed) = 20,000 kg-m/s
"Impulse" is (force exerted) x (time the force lasts)
and it's equal to the change in momentum.
(Force) x (10 sec) = 20,000 kg-m/s
Divide each side by (10 sec) and you have
Force = (20,000 kg-m/s) / (10 sec)
= 2,000 kg-m/s² = 2,000 Newtons
