The momentum of an object is calculated using the following formula:

Momentum (p) = Mass (m) × Velocity (v)

In this case:

* Mass (m) = 20 kg

* Velocity (v) = 8 m/s

Therefore, the momentum of the dog is:

* p = 20 kg × 8 m/s = 160 kg m/s

The momentum of the 20 kg dog running at 8 m/s is 160 kg m/s.