When approaching a traffic light, the car reduced its speed from 43.2 km / h

When approaching a traffic light, the car reduced its speed from 43.2 km / h to 28.8 km / h in 8 seconds. Determine acceleration and braking distance.

Problem data: V0 (initial vehicle speed) = 43.2 km / h (in SI V0 = 12 m / s); V (final speed) = 28.8 km / h (in SI V = 8 m / s); t (deceleration time) = 8 s.

1) Vehicle acceleration: a = (V – V0) / t = (12 – 8) / 8 = 0.5 m / s2.

2) Braking distance: S = (V ^ 2 – V0 ^ 2) / 2a = (12 ^ 2 – 8 ^ 2) / (2 * 0.5) = 80/1 = 80 m.

Check: S = (V + V0) * t / 2 = (12 + 8) * 8/2 = 160/2 = 80 m (correct).

Answer: Acceleration is 0.5 m / s2; the braking distance is 80 m.