Mathematical & Physical Principles of Reconstruction Flashcards

A vehicle skids to a stop leaving 120 feet of skid marks on a road with a drag factor of 0.75. Using the skid-to-stop formula, what was the approximate minimum speed?

Answer: 51.5 mph

Using S = √(30 × d × f) = √(30 × 120 × 0.75) = √2700 ≈ 51.96 mph, which rounds to approximately 51.5 mph.

In projectile motion analysis of a vehicle that launches off a cliff, which two components of initial velocity are treated as independent?

Answer: Horizontal and vertical

Projectile motion treats horizontal velocity as constant (no air resistance assumed) and vertical velocity as independently accelerated by gravity.

What is the centripetal acceleration of a vehicle traveling at 60 ft/s around a curve with a radius of 300 feet?

Answer: 12.0 ft/s²

Centripetal acceleration a = v²/r = (60)²/300 = 3600/300 = 12.0 ft/s².

Conservation of momentum in a two-vehicle collision is valid only when:

Answer: No external forces act on the system during impact

Conservation of momentum applies when the net external force on the system is zero, meaning no significant external forces act during the brief impact interval.

A vehicle with a weight of 3,200 lbs has a coefficient of friction of 0.72 with the road. What is the maximum frictional braking force available?

Answer: 2,304 lbs

Frictional force = weight × coefficient of friction = 3,200 × 0.72 = 2,304 lbs.

When calculating the speed from yaw (critical curve) marks, the reconstrutionist uses which primary formula?

Answer: S = √(15 × r × e+f)

Critical speed for a yaw mark is S = √(15 × r × (e + f)), where r is the radius of curvature, e is superelevation, and f is side friction.

The coefficient of restitution (e) for a perfectly plastic (inelastic) collision equals:

Answer: 0.0

A perfectly plastic collision means the objects stick together with no rebound, so e = 0, indicating zero relative velocity after impact.