To a police investigator, skid marks evidence is extremely important in determining how vehicles moved in a collision. Skid marks are the equivalent of fingerprints 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 equals square root of 30 times D times f times n end root

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

If a car’s speed is 70 miles per hour on a road surface with a drag factor of 0.50 and with a breaking efficiency of 85% (n = .85), what would be the length of the skid marks? Round to the nearest tenth.

450.6

482.4

463.2

384.3