When the reaction has passed 3s, the distance is already150-250/9 * 3 = 200/3 m.
At this time, time 200/3/250/9 = 12/5 and 2.4s are obtained by dividing distance by speed.
Question 2: First of all, let's calculate how long it takes to cross the overpass 40/1.25 = 32 s.
It takes 30 seconds to cross the zebra crossing, which means it only takes 2 seconds to cross the zebra crossing.
And the street width of 30m, that is, 30/2 = 15 m/s, is definitely impossible as a normal person.
The third question: because there is a distance of 20 to 30 meters from the car in front, that is to say, choose the critical point of 20m &；; 30 meters
When you stop, you should turn on 10m, which means that your reaction time is only10m&; 20 meters
Divide the driving distance by your time, and you can get the required driving speed 10/3 m/s, 12km/h 20/3 m/s, 24 km/h.
Answer the above, I hope you like it.