ACTAR Mathematical & Physical Principles of Reconstruction

Question 1

What physical principle explains conservation of motion in crashes?

Accepted Answer

Conservation of momentum

Answer

The physical principle of conservation of momentum states that the total momentum of a system remains constant before and after a collision, assuming no external forces. In crash reconstruction, this principle is fundamental for analyzing how forces are transferred between vehicles and for calculating their speeds and directions before and after impact.

Question 2

What equation estimates speed from skid marks?

Accepted Answer

S = √(30 × d × f)

Answer

The equation S = √(30 × d × f) is a standard formula used in crash reconstruction to estimate a vehicle's speed (S) based on the length of its skid marks (d) and the drag factor (f) of the road surface. This formula is a critical tool for determining pre-braking speeds and understanding crash dynamics.

Question 3

What does Newton’s Second Law state?

Accepted Answer

Force equals mass times acceleration

Answer

Newton's Second Law of Motion states that force equals mass times acceleration (F=ma). This principle is fundamental in crash reconstruction for understanding how forces applied during an impact cause changes in a vehicle's motion, allowing investigators to calculate impact forces based on vehicle mass and observed acceleration or deceleration.

Question 4

Why is drag factor important?

Accepted Answer

It influences deceleration rate

Answer

Drag factor is important because it represents the coefficient of friction between a vehicle's tires and the road surface, directly influencing the vehicle's deceleration rate. A higher drag factor indicates greater friction, leading to faster deceleration, which is a critical input for calculating speeds from skid marks in crash reconstruction.

Question 5

What unit is acceleration typically measured in?

Accepted Answer

Feet per second squared

Answer

Acceleration is the rate at which an object's velocity changes over time. In the imperial system, commonly used in some reconstruction contexts, acceleration is typically measured in feet per second squared (ft/s²), precisely quantifying how much an object's speed changes each second.

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

ACTAR Mathematical & Physical Principles of Reconstruction