Cruise Control dangerous 5266On Fri, 11 Mar 2005 21:52:37 -0000, "Clive George" No, they would have to slip relative to the ground they were rotating over - that...
John Laird
Conservation of momentum. Kinetic energy will not be conserved provided that the crumple zones work properly since a lot of energy will be absorbed breaking the spot welds and bending metal. This has the effect of slowing the duration and softening the impact for both parties. 2mph change in velocity might also be a bit high - I buttumed simple round numbers so the car is a bit on the heavy side. I'll detail my buttumptions here so they can be dissected:
Car weight 2T (high) relative speed 40mph = 64kph = 18m-s Truck weight 40T relative speed -2mph = -3.2kph = -1m-s
buttume perfectly inelastic collision (optimistic) but probably nearer to the truth than perfectly elastic (get twice the acceleration for this) - the true answer probably lies somewhere inbetween these limits.
Car deceleration is 18-0.1 = 180m-s^2 = 18g Truck acceleration is 1-0.1 = 10m-s^2 = 1g
It is likely at this lateral acceleration that the tyres will skid and the trailer frame will flex and compress to take up some of the impulse. Thus slowing down the rate of acceleration at the cab end.
I believe this may be possible but nearer +1mph. The only collision in this clbutt I know of locally was a fast lad at 70+mph (100?) glancing off the corner-side of a slow fully laden silage trailer at night. The latter didn't notice at the time but had slight damage to tail lights and minor bends when inspected. Everyone in the car was end.
Are you sure? That seems a bit on the high side.
I reckon the effect of the crumple zones and road friction will soften it to around 0.2s elapsed time and ~0.5g at the rear end. But the lorry frame and coupling isn't rigid under that sort of impulse so the shock transmitted to the cab and driver will be less. It is possible the truck driver did feel something and wondered what happened but seeing nothing untoward kept on going leaving the mangled heap in his blind spot.
The deceleration imparted to the car by the impulsive force will be larger by the ratio of the two vehicle mbuttes so perhaps somewhere around 20g peak... and that is seriously bad for you.
Seems like there should be some experimental numbers on TRL website or elsewhere but a quick check didn't find any.
Cruise Control dangerous 5265On 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...
Cruise Control dangerous 5268somewhere. than you I think you're looking at the lorry & car as an isolated system, in which case you are perfectly correct in your buttertion of conservation of moment between the two. I'd still maintain...
Regards, Martin Brown
