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Author Topic: Calculation of impact velocity  (Read 13112 times)
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HACKNEYL
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on: June 05, 2008, 04:40:45 am » posted from:Pretoria,Gauteng,South Africa

Hi All

I enjoyed posts of reaction time calculations & simulations of stopping distance.  My question is:  Two cars drive along.  The front one at 100km/h. He gets hit from behind by a car with speed far exceeding that of the front car.  The brake marks of the car behind measure 65m.  Can we somehow calculate/estimate the speed of the rear car at the point of of impact and at point where he started braking?  Both cars where average size family cars (max 5 persons) only 1 person in rear car.  Had ABS brakes.  Tyres in very good condition. How much impact would road & air temperature as well as tyre temperature have on the result?

Kind regards!
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Fu-Kwun Hwang
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Reply #1 on: June 05, 2008, 10:12:44 am » posted from:Taipei,T\'ai-pei,Taiwan

Need to know the friction coefficient of tires.
If that car fully stopped without hit the front car, and assume friction coefficient is 1.0, then v2=2*a*s=2*9.8*1.0*65=1274
So estimated speed v=35.7m/s = 128 km/hr.

The speed could be larger, if the coefficient is larger than 1 (normally, yes) and the front car gets hit from behind!
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