How long can it take to stop a car moving at a speed of 72 km / h if the acceleration is 5 m / s2

How long can it take to stop a car moving at a speed of 72 km / h if the acceleration is 5 m / s2 during fast braking? What is the braking distance?

To find out how long it takes t to stop a car moving at a speed of v₀ = 72 km / h = 20 m / s, if during rapid braking it moved with acceleration a = – 5 m / s ^ 2 and its final speed v = 0 m / s, we use the formula:

t = (v – v₀) / a or

t = (0 m / s – 20 m / s) / (- 5 m / s ^ 2);

t = 4 s.

In this case, the braking distance S is determined using the formula:

S = v₀ ∙ t + a ∙ t² / 2 or

S = 20 m / s ∙ 4 s + (- 5 m / s ^ 2) ∙ (4 s) ² / 2;

S = 40 m.

Answer: the car will stop in 4 seconds; the braking distance will be 40 meters.