85.0 km/h = 23.61 m/s
52.8 km/h = 14.67 m/s
Total distance = reaction time distance + braking distance
= V*t + V^2/(2a)
Write two equations in two unknowns and solve for the two unknowns, a and t.
56.7 = 23.61 t - (23.61)^2/(2a)
24.4 = 14.67 t - (14.67)^2/(2a)
To stop a car, first you require a certain reaction time to begin braking. Then the car slows down at a constant rate. Suppose that the total distance moved by your car during these two phases is 56.7 m when its initial speed is 85.0 km/h, and 24.4 m when the initial speed is 52.8 km/h.
(a) What is your reaction time?
(b) What is the magnitude of the deceleration?
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