Question

You are driving on an asphalt road that had a 40 mi/h speed limit. A bicyclist veered into your lane so you slam on your brakes. Your tires left three skid marks of 69 ft, 70 ft, and 74 ft. The road had a drag factor of 0.95. Your brakes were operating at 98% efficiency. The police gave you a ticket for speeding. You insist that you were driving under the speed limit. Who is correct?

Answer 1

Answer:

Policeman is correct.

Step-by-step explanation:

Consider the provided information.

The tires left three skid marks of 69 ft, 70 ft, and 74 ft.

The road had a drag factor of 0.95. Your brakes were operating at 98% efficiency.

Thus, drag factor (f) = 0.95 and brakes efficiency (n) = 0.98

Compute the skid distance by finding the mean of length of 3 skids.

$D=\frac{69+70+74}{3}\\D=\frac{213}{3}\\D=71$

Therefore, the skid distance is 71 ft.

Now find the speed of car using skid speed formula:

$S=\sqrt{30Dfn}$

Where, S is the speed of car, D is the skid distance, f is the drag factor and n is the beak efficiency.

Substitute the respective values in above formula.

$S=\sqrt{30\times 71\times0.95 \times0.98}$

$S=\sqrt{1983.03}$

$S\approx 44.5312$

Your speed was 44.5312 mi/h which is greater than 40 mi/hr.  So policeman is correct.