With emergency braking, a vehicle moving at a speed of 72 km / h stopped after 5 seconds. Find the braking distance.

Initial data: V0 (speed before emergency braking) = 72 km / h; t (time to stop) = 5 s.
SI system: V0 = 72 km / h = 20 m / s.
1) Determine the acceleration with which the emergency braking occurred: V = V0 + a * t, whence a = -V0 / t = -20 / 5 = -4 m / s ^ 2 (acceleration modulus a = 4 m / s ^ 2 ).
2) Braking distance: a) S = V0 * t + a * t ^ 2/2 = 4 * 5 ^ 2/2 = 50 m.
b) S = (V ^ 2 – V0 ^ 2) / 2a = -V0 ^ 2 / 2a = -20 ^ 2 / (2 * (-4)) = -400 / (-8) = 50 m.
Answer: The braking distance during emergency braking was 50 m.