Question

Here's a tricky but simple one...Compare these two collisions and identify which one is worse.

1) Two identical cars traveling at 60 mph in opposite directions toward each other collide head-on.

2) One car traveling at 60 mph collides with an immovable concrete wall.

Which collision is worse and why?

(Warning: Marilyn vos Savant got this wrong.)

Answer 1

Trick question! They will both suffer the same for each.

This is becuase on a 60mph collision for 1 car it will suffer 60mph damage, but when on a 60mph 2 car collision, they will still suffer 60mph each as the overall fore is distributed 50/50.

The Mythbusters did an episode on this!

Answer 2

Yah. Newton's third law - regarding equal and opposite reaction. The brick wall has a practical unlimited quantity of potential energy, just enough of which it converts to kinetic to equal that applied by the single car during the collision.

In the two car episode, each car applies the exact same amount of kinetic energy during the collision.

The mph is not how we would measure this however, because it could involve a car weighing half as much, but going 1.414 times as fast, as

\[K.E = 1/2 m v^{2}\]

Answer 3

I'd say that in the cars coming at each other, that's equivalent to one car still and the other on 120mph. Compared to 60 into a brick wall ... this is "hobson's chioice" ???

Answer 4

this is supposed to be a physics forum, i think, so maybe there is a metric for 'worse" ?!

:-)

Answer 5

oh heavens, shamrock's humour strikes again ! A metric for "worse". How about the loudness of the impact, or the intensity of the fireball, or something ?

Answer 6

i was being kinda serious "in a friendly way" :-)

emoticon mix-up?!

the question is: "Compare these two collisions and identify which one **is worse**."

Your metric idea is kinda there - cars come with crumple zones so engineers think they must "soften the blow". The question should therefore be couched in terms of rates of change of momentum or rate of change or energy into thermal and sound as you say

just saying.....worse for the drivers, we can guess that. what is worse? in physics terms.

Answer 7

The first one is worse because you are going to destroy 2 cars and possibly the drivers too. Oh yeah! there is also double the kinetic energy which results in double the damage. I presume the immovable wall will not be altered by the hit or something did indeed move.