The answer is a bit less than 50 m. To get this result:
We assume the road is flat and dry.
Moreover, we assume an average perception-reaction time of 2.5 seconds.
We apply the stopping distance formula, which (under our assumptions) reads:
s = (0.695 × v) + (v² / 177.8).
Here, v denotes the car's speed in km/h.
Plugging in v = 50, we get 48.81 m.
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