>> OK, I thought about it this way, maybe you're right. If you were in a
>> stationary vehicle (or even a stationery vehicle if you were delivering
>> office supplies) and a car hit you at 75mph, that would sting. So if you
>> were travelling at 75mph also and hit head-on.......
>>
>> What I'd reasoned was that at the point of impact you as a vehicle have
>> deccelerated from 75 to 0 and stopped at exacty the same point you
>> would have if you'd hit a stationary wall. Hmmm, still not convinced
>> about that "combined speed" thing

> Umm, sure in both cases you decelerate from
> 75 to 0, but when you hit the oncoming car you
> decelerate twice as fast?? That's bad. :o)

No.  Why would you decelerate twice as fast?  The occupants
of each vehicle are moving at 75MPH -- no faster.  Each one
decelerates to 0MPH.  If the vechicles are _equal mass_ and
collide with perfectly aligned force vectors, then it is
symmetrical.  Each vehicle consumes 1/2 of the kinetic energy
and experiences the same deceleration as hitting a huge
immovable object.

                                                Lee Jones

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