On dry concrete, a car can decelerate at 6.0m/s2, whereas on wet concrete it can decelerate at only 5.0m/s2.

Question

(a) Find the distance necessary to stop a car moving at 24.0m/s24.0m/s on dry concrete.

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(b) Find the distance necessary to stop a car moving at 24.0m/s24.0m/s on wet concrete.

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(c) Repeat both calculations, finding the displacement from the point where the driver sees a traffic light turn red, taking into account his reaction time of 0.5s0.5s to apply the brakes.

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Answer 1

For a and b, you can use the equation V^2 = V_o^2 - 2aD where V is the final velocity (0), V_o the initial velocity, a the deceleration, and D the distance traveled. Just use the appropriate values for a and solve for D.

For part c, add the distance traveled during the reaction time using D = 24.0 m/s x 0.5 s to the results for a and b.