How much force does it take to stop a 1,000 kg car traveling at 20 m/s in 10 seconds?

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