A heavy truck moving at a speed v has much more momentum than a skateboard moving at the same speed, because of the truck's large mass. Therefore, the impulse (change in momentum) required to stop the massive truck is much more than the impulse required to stop a skateboard moving at the same speed. If the skateboard is stopped very quickly, the force required can be quite large. A force smaller than this amount, but applied over a long time can eventually stop the moving truck. A large impulse can be delivered if a force is allowed to act over a long time.