>In your example the light vehicle would be accelerated from zero to (say) 50 km/h in the length of its rear crumple zone. It's not impossible to manage that; YouTube has examples of stock and Indy cars hitting the wall at 150+ km/h (accelerating from that speed to zero in the length of that vehicle's crumple zone) with the driver basically walking away.

The crash Alonso walked away from this weekend really was spectacular, but F1 cars do not sell cheap -))