Acar is traveling at 100 km/h when the driver sees an accident 80 m ahead and slams on the brakes. what minimum constant deceleration is required to stop the car in time to avoid a pileup? (round your answer to two decimal places.)

Assuming the driver starts slamming the brakes immediately, the car moves by uniformly decelerated motion, so we can use the following relationship
(1)
where 
a is the deleceration
S is the distance covered after a time t
is the velocity at time t
is the initial speed of the car

The accident is 80 m ahead of the car, so the minimum deceleration required to avoid the accident is the value of a such that S=80 m and  (the car should stop exactly at S=80 m to avoid the accident). Using these data, we can solve  the equation (1) to find a:

And the negative sign means it is a deceleration.