You are driving on a narrow road. About 20 m ahead of you a child suddenly runs onto the roadway. When is a collision unavoidable despite emergency braking?

If you are driving at 50 km/h and a child suddenly runs onto the road just 20 meters ahead, it is nearly impossible to stop in time, even with emergency braking. This is because at higher speeds, both your reaction distance (the distance your car travels during your reaction time before you start braking) and braking distance (the distance needed to come to a complete stop after braking begins) are much longer. At 50 km/h, the sum of these distances easily exceeds 20 meters, making a collision unavoidable.

At lower speeds like 30 km/h or 20 km/h, your stopping distance would be shorter, increasing your chances of stopping in time. This is why driving slower is especially important near places where children might suddenly appear, such as residential areas or near schools. In summary, the correct answer is 50 km/h because at that speed, stopping within 20 meters is not possible, while at lower speeds it might be.