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Deceleration over a known distance comes from v^2 = u^2 + 2as rearranged, which avoids needing the time. Braking from 100 km/h to 5 m/s in 60 m demands about 6.2 m/s2, or 0.63 g. Because kinetic energy goes as speed squared, most of the energy is removed in the first part of the stop.
From speeds and distance
a = (v^2 - u^2) / (2s)
Time to slow
t = (v - u) / a
Stopping distance goes with the square of speed, so twice the speed needs four times the distance at the same deceleration.
Around 0.8-1.0 g on dry asphalt with good tyres, roughly 8-10 m/s2. Wet roads cut that by a third or more.