The car, moving evenly, travels 32 m in 4 seconds. After that, the car starts braking to a complete stop.

The car, moving evenly, travels 32 m in 4 seconds. After that, the car starts braking to a complete stop. What is the acceleration of the car when braking if the stopping distance of the car is 6.4 m.

Condition:
S1 = 32 m.
t = 4 s.
S2 = 6.4.
To find :
a -? m / s ^ 2
Decision :
S1 = V * t
V = S1 / t
[V] = m / s = m / s.
V = 32/4 = 8 (m / s).
V is the initial speed.
V2 is the final speed.
S2 = V2 ^ 2-V ^ 2 / 2a .- since V2 = 0 m / s – the car has stopped.
Follows that :
S2 = – V ^ 2 / 2a – because the movement is equally slow.
6.4 * 2a = -8 ^ 2.
12.8a = 64.
a = 5 m / s ^ 2.
Answer: 5 m / s ^ 2.