PHYSICS HELP! reaction time

Question

What role does reaction time play in applying the brakes to your car in emergency situations? Assume your car is traveling at 100 kph when a pedestrian suddenly crosses the street in front of your car. How far will your car travel before you can apply the brakes?

I used this as a solution:

x(t) = 1/2aot2 + vot + xo

x(t) = 0 + vot + 0

x(t) = vo= 100 km/1 hr= 100000m/3600s = 27.8 m/s (t)

However I was told that the equation was wrong! Please help

Answer 1

You will travel at 100 kph until you can apply the brakes.

Mean human reaction time is about 0.25 s (Google this to confirm).

So car travels 100 kph for 0.25s before brakes are applied.

100 kph = 100 k / 3600 kps = 100000/3600 m/s

So in 0.25s you travel 0.25 x (100000 / 3600) m = 6.94 m.