When approaching a traffic light, the car reduced its speed from 36 km / h to 0 km / h in 4 seconds.

When approaching a traffic light, the car reduced its speed from 36 km / h to 0 km / h in 4 seconds. Determine its acceleration and braking distance.

Initial data: V0 (initial vehicle speed) = 36 km / h; V (car speed at a traffic light) = 0 km / h; t (braking time) = 4 s.
SI system: V = 36 km / h = 36 * 1000/3600 m / s = 10 m / s.
1) We calculate the acceleration of the car (the movement is slowed down and a <0):
V = V0 + a * t; a * t = -V0.
a = -V0 / t = -10 / 4 = -2.5 m / s ^ 2.
2) Determine the braking distance of the car:
S = V0 * t + a * t ^ 2/2 = 10 * 4 – 2.5 * 4 ^ 2/2 = 40 – 20 = 20 m.
Answer: Acceleration of the car modulo 2.5 m / s ^ 2; the braking distance was 20 m.