text: approximately how long are the skid marks of the car that is going 65 miles per hour? at the scene of a traffic accident, a police investigator must determine the speed of both vehicles. the investigator uses the formula s= sq root 5l where s represents speed, measured in miles per hour, and l represents the length of the skid marks, measured in feet. approximately how long are the skid marks of the car that is going 65 miles per hour? s^2 = 5l l = s^2/5 =65*65/5 = 65*13 = 650 + 130 + 65 (fast reckoning) = 845 feet  ---  in fact i am not so easy with miles and feet: i know it by km as they teach in italy: lenght of stop = approx. (speed/10)^2  so speed = sqrt(lenght)*10 lenght in km; speed in km/h