60kmh then u brake and bang divider at 20-30 also wont fly so dramatically right?

impulse = change of momentum per time
F = ^m / t

loosely translated, the change in velocity (c.o.momentum) is the same since it is (velocity at impact -> decelerating to 0), but we can vary the time taken for the deceleration (t)..by making the c.o.m divided by a larger time (t) value, the force (F) experienced by passengers in the car is lessened.

one effective way of increasing t value is to make sure there's a crumple zone.