The equation for time in seconds is t = Ve – Vi / a
Where:
Ve = velocity ending = 0 fps
Vi = velocity initial = 45 mph / 65.97 fps
a = acceleration rate fps²
The average deceleration rate range for dry asphalt is -17.71 to -22.54 fps²
t = 0 – 65.97 / -17.71 = 3.725 seconds
t = 0 – 65.97 / -22.54 = 2.926 seconds
The above equation is using the average. To use the 70 foot skid mark, we would use the acceleration equation a = Ve² - Vi² / 2d
Where:
Ve = velocity ending = 0 fps
Vi = velocity initial = 45 mph / 65.97 fps
a = acceleration rate fps²
d = distance
a = O² - 65.97² / (2*70)
a = -4352.0409 / 140
a = -31.08 fps²
use the calculated a in the first equation gives you the exact time
t = 0 – 65.97 / -31.08
t = 2.122 seconds