V0 = 90 km / h = 25 m / s. V = 0 m / s. t = 4 s. S -? For uniformly accelerated movement, in which braking occurs, the path S traversed by the body is determined by the formula: S = V0 * t – a * t ^ 2/2, where V0 is the speed at the beginning of braking, t is the braking time, a is the acceleration during braking. We find the acceleration of motion a by the formula: a = (V – V0) / t. a = (0 m / s – 25 m / s) / 4 s = – 6.25 m / s ^ 2. The “-” sign means that the acceleration is directed against the direction of the velocity, the body is decelerated. S = 25 m / s * 4 s – 6.25 m / s ^ 2 * (4 s) ^ 2/2 = 50 m.
Answer: the braking distance of the car was S = 50 m.
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