Cruise Control dangerous 5265

On Sat, 12 Mar 2005 10:14:31 +0000, Martin Brown

I buttume you arrived at a collision duration of 0.1s by dividing the crumple zone by the relative speed, but you forgot to double it as the average relative speed during impact is of course half the original value. So you should in fact have 9g and 0.5g for the two vehicles. On the other hand, I think 2m of crumple zone is overly generous. Almost all of this must be in the car, but that would intrude well into the pbuttenger compartment.

Only the driven wheels have any resistive force available, to whit the engine braking available as the revs rise, but fuelling doesn't. The undriven wheels should be free to accelerate as bearing friction will be negligible.

Posting too late at night ;-)

Me neither, so we are left with first principles and buttumptions. I reworked some numbers in my head, using a closing speed of 31km-h, relative vehicle mbuttes of 1:30, and a 1m crumple zone. Deceleration for the car driver, buttuming inelastic collision so that the car doesn't slow down to less than the truck speed while they are in contact, is 3.8g, and of course 1-31 of that for the truck, which is 0.12g. Collision time is just under 1-4s. It's not easy to guess whether the truck driver will notice that brief moment of acceleration as his vehicle gains 1km-h of speed, however to put it into context, a 44t truck at 90km-h would need an engine supplying nearly 5000kWh to the wheels, or nearly 6500bhp, to accelerate at that rate. I can't see that being mistaken for a "surge". However, the cab suspension may provide some degree of damping.

-- Never argue with a fool - people might not know the difference.

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