A car of mass 2400kg moving at 20 m/s slams into a cement wall and comes to a halt?

Impulse = change in momentum

The car's momentum was (mass) x (speed)

Momentum = (2400 kg) x (20 m/s)

Momentum = 48,000 km-m/s

To completely stop the car, the impulse = - 48,000 km-m/s.