Car moving For a certain period of time at a speed of 90 m / s, its speed decreases to 72 km / h

Car moving For a certain period of time at a speed of 90 m / s, its speed decreases to 72 km / h on a path length of 56.25 4 m. What is the acceleration of the car during braking and the braking time.

Initial data: V0 (initial vehicle speed) = 90 m / s, V (vehicle speed after braking) = 72 km / h or 15 m / s, S (braking distance) = 56.254 m, equally slow motion (a <0).

1) Let’s calculate the acceleration of the car:

S = (V² – V0²) / 2a.

S * 2a = V² – V0².

a = (V² – V0²) / 2S = (202 – 902) / (2 * 56.254) = -68.44 m / s2.

2) Let’s calculate the braking time:

V = V0 + a * t.

t = (V – V0) / a = (20 – 90) / (-68.44) = 1.02 s.

Answer: Vehicle acceleration module 68.44 m / s2, deceleration time 1.02 s.