To stop a car, first you require a certain reaction time to begin braking; then

Question

To stop a car, first you require a certain reaction time to begin braking; then the car slows under the constant braking deceleration. Suppose that the total distance moved by your car during these two phases is 50.6 m when its initial speed is 79.1 km/h, and 21.9 m when its initial speed is 47.9 km/h. What are (a) your reaction time and (b) the magnitude of the deceleration?

Explanation / Answer

let reaction time = t deceleration = a 1> 79.1 km/h = 22 m/s 22t + 22^2 / 2a = 50.6 2> 47.9 km/h = 13.3 13.3 t + 13.3^2 /2a = 21.9 solving we get reaction time = 0.65 s deceleration = 6.66 m/s^2

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