# NTNUJAVA Virtual Physics LaboratoryEnjoy the fun of physics with simulations! Backup site http://enjoy.phy.ntnu.edu.tw/ntnujava/

## JDK1.0.2 simulations (1996-2001) => kinematics => Topic started by: HACKNEYL on June 05, 2008, 04:40:45 am

 Title: Calculation of impact velocity Post by: HACKNEYL on June 05, 2008, 04:40:45 am Hi AllI 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! Title: Re: Calculation of impact velocity Post by: Fu-Kwun Hwang on June 05, 2008, 10:12:44 am 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=1274So 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!