Here's why:

* Momentum is a measure of an object's mass in motion. It's calculated by:

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

* If both vehicles have the same velocity, the only factor affecting their momentum is their mass.

* A heavier vehicle, even at the same speed, will have more momentum because it has more inertia (resistance to change in motion).

Example:

* A small car (low mass) and a large truck (high mass) traveling at the same speed. The truck will have much greater momentum due to its larger mass.