The momentum matters when you hit something. A large truck has a lot more momentum than a small car. If it hits something it needs proportionally more force to stop it. Since forces are equal and opposite, that means the hit object has to absorb more force. Basically thing of the difference between someone dropping a marble on your head from a balcony to doing the same with a bowling ball. It’s the same with a child hit by a vehicle.
For passengers, only their mass matters. Whether you’re in a car, a truck, a train or an ocean liner, all that matters is the person’s mass and the rate of change.
The momentum matters when you hit something. A large truck has a lot more momentum than a small car. If it hits something it needs proportionally more force to stop it. Since forces are equal and opposite, that means the hit object has to absorb more force. Basically thing of the difference between someone dropping a marble on your head from a balcony to doing the same with a bowling ball. It’s the same with a child hit by a vehicle.
For passengers, only their mass matters. Whether you’re in a car, a truck, a train or an ocean liner, all that matters is the person’s mass and the rate of change.