Question

To a police investigator, skid marks evidence is extremely important in determining how vehicles moved in a collision. Skid marks are the equivalent of a fingerprint in a criminal investigation, and just as important. The speed a car was traveling can be calculated using the skid marks made as the car came to a stop. The formula for finding the speed of the vehicle is:

S= √30.D.f.n
Where:
S = speed in miles per hour
30 = a constant value used in the equation
D = length of the skid marks in feet
f = drag factor for the road surface
n = braking efficiency as a percent
A car skids to a stop, leaving five skid marks with an average length (D) of 50 feet. The road is asphalt. Skid tests reveal a drag factor (f) of 0.65. Since all four wheels were braking, the braking efficiency (n) is 100% or 1.00. To the nearest mile per hour, what was the car’s speed at the time of the accident?

Answer 1

The formula for finding the speed of a vehicle using skid marks is S = √(30 · D · f · n). For the given scenario, the car's speed was approximately 18 mph at the time of the accident.

Step-by-step explanation:

The formula for finding the speed of a vehicle using skid marks is:

S = √(30 • D • f • n)

Where:
S = speed in miles per hour
D = length of the skid marks in feet
f = drag factor for the road surface
n = braking efficiency as a percent

For the given scenario, the skid marks have an average length of 50 feet, the drag factor for the road surface is 0.65, and the braking efficiency is 100%. Thus, the speed of the car at the time of the accident can be calculated as:
S = √(30 • 50 • 0.65 • 1.00) = 18.34 mph
Rounding to the nearest mile per hour, the car's speed was approximately 18 mph at the time of the accident.