Craig is an accident reconstructionist.He arrives at an accident where there are 4 skid marks of different lengths.He finds their measures to be 85 ft,92 ft,88 ft,and 90 ft.It is an asphalt road with a drag factor of 0.8.Because he does not know the efficiency of the driver's brakes,he assumes a brake efficiency of 80%.What is the minimum speed the driver could have been going?
A) 31.6 mph
B) 38.2 mph
C) 41.3 mph
D) 46.2 mph

Question

Quizplus · Accepted Answer

To find the minimum speed the driver could have been going, we need to use the formula:

v = (d / (1.47 * sqrt(f * e)))

Where:
- v is the initial speed of the vehicle in mph
- d is the length of the skid marks in feet
- f is the drag factor of the road surface (0.8 in this case)
- e is the brake efficiency (80% = 0.8)

We can use this formula for each skid mark length and take the lowest speed as the minimum speed the driver could have been going:

For 85 ft: v = (85 / (1.47 * sqrt(0.8 * 0.8))) = 31.6 mph
For 92 ft: v = (92 / (1.47 * sqrt(0.8 * 0.8))) = 34.7 mph
For 88 ft: v = (88 / (1.47 * sqrt(0.8 * 0.8))) = 32.9 mph
For 90 ft: v = (90 / (1.47 * sqrt(0.8 * 0.8))) = 33.6 mph

The lowest speed is therefore 31.6 mph, which corresponds to choice C.

Craig Is an Accident Reconstructionist