While driving a car, you see an obstruction in the road. It takes you 0.80 seconds to react and put your foot on the brake. The car is travelling at 25 m/s. If, when the brakes are applied, the acceleration is 9.3 m/s^2 [backwards], what is the total displacement of the car?

Answer 1

How long does it take to stop after brakes pressed:
vf=vi+at or t= 25/9.8
how far does it travel then?
d=avgvelocity/time=12.5*9.8/25=4.9 m
how far did it travel in reaction time?
d=25/.8
now add the two distances.