Topic: IIHS Trucks test

[Sir Osis of Liver]

The infinite mass barrier collision test replicates the forces involved of two identical cars hitting at identical but opposite speeds.
A JCW mini hitting the barrier at 30mph would experience the same forces as two JCW minis having a head on while they were each travelling at 30mph.

Should it be a mini hitting the barrier at 60 mph? The total energy of a mini hitting a barrier at 60 mph should be equivalent to the total energy of two minis travelling 30 mph hitting each other. Or am I missing something?

Both cars deform and dissipate energy, where the wall doesn't and the single car has to absorb all the energy. So two deformable objects colliding at the same speed dissipate the same energy as one deformable object hitting a wall. 

Mythbusters did a good segment on it.

https://www.youtube.com/watch?v=r8E5dUnLmh4

[Hannibalsmith]

The infinite mass barrier collision test replicates the forces involved of two identical cars hitting at identical but opposite speeds.
A JCW mini hitting the barrier at 30mph would experience the same forces as two JCW minis having a head on while they were each travelling at 30mph.

Should it be a mini hitting the barrier at 60 mph? The total energy of a mini hitting a barrier at 60 mph should be equivalent to the total energy of two minis travelling 30 mph hitting each other. Or am I missing something?

Both cars deform and dissipate energy, where the wall doesn't and the single car has to absorb all the energy. So two deformable objects colliding at the same speed dissipate the same energy as one deformable object hitting a wall. 

Mythbusters did a good segment on it.

https://www.youtube.com/watch?v=r8E5dUnLmh4

True on the dissipation of energy. I guess I was more thinking more from a conservation of energy perspective, but I think you are focusing on the force on only one mini...

[Sir Osis of Liver]

Each car has kinetic energy KE=1/2MV². Since they are equal and opposite the cars come to a stop at the point of impact over the distance of their respective crumple zones.

With a car hitting an immovable, undeformable wall, it comes to a complete stop at the point of impact over the distance of its crumple zone.

If the speed prior to impact was doubled, the KE ends up being four times as large due to the V² term.

[ElectricMayhem]

Counterintuitive, but yah, in crash testing 40 mph + 40 mph = 40 mph.