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Originally Posted by Brazen
I cant believe I am disagreeing with a Physics doctorate but I am..
If you assume a perfectly inelastic collision, there is no difference between hitting a unyielding brick wall OR an identical car of the same mass travelling toward you at the same speed. Its conservation of momentum - and you can take that to the bank!
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Conservation of momentum would mean the wall has to transfer the energy for any rebound. If the wall is totally inert, immoveable, invulnerable etc this can't happen, so because the momentum must be conserved and the only way it can go is into whatever is anchoring the wall = the planet.
If we place the same caveats on the cars and say they don't have any absorption and momentum must be retained, they are travelling at 100kph initial speed, but after butting heads and bouncing off each other they have a final velocity of -100kph. Put that into the V-V1 formula (100 --100) and you get 200 kph for the energy function of each. Deduct whatever you want for absorption after that.