There are several equations and rules of thumb for estimating the braking distance of a car. The distance increases as the vehicle momentum increases.
Parameters:
(1) initial velocity
(2) reaction time in seconds (often taken as 1.5 seconds)
(3) road surface friction coefficient (often taken as 0.7 but potentially lower or higher)
total braking distance =
= ((velocity) * (reaction time)) + (((velocity)^2) / (2 * (friction coefficient) * (gravity)))
Alternatively, a rule of thumb (Wikipedia) may be used:
distance in feet =
= (((INT((mph)/10))^2) * 5) + (2 * (mph))
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Specialty: Emergency Medicine