The magnitude of the car's momentum is what you're looking for. Here's how to calculate it:

Momentum (p) = mass (m) × velocity (v)

* m = 400 kg

* v = 30 m/s

p = 400 kg * 30 m/s = 12,000 kg·m/s

Therefore, the magnitude of the car's momentum is 12,000 kg·m/s.