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

Policeman is correct.

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=(69+70+74)/(3)\\D=(213)/(3)\\D=71`

Therefore, the skid distance is 71 ft.

Now find the speed of car using skid speed formula:

`S=√(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=√(30* 71*0.95 *0.98)`

`S=√(1983.03)`

`S\approx 44.5312`

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