ACTAR Crash Dynamics 3

Question 1

Which physical principle explains why an unrestrained occupant continues moving forward at the vehicle's pre-crash speed when the vehicle suddenly decelerates?

Accepted Answer

Newton's First Law (inertia)

Answer

Newton's First Law states that a body in motion continues at constant velocity unless acted upon by a net force; an unrestrained occupant lacks the restraining force the seatbelt would provide.

Question 2

When analyzing a low-speed rear-end collision, which factor most significantly affects the magnitude of delta-V experienced by the struck vehicle?

Accepted Answer

Mass ratio between the striking and struck vehicles

Answer

The mass ratio between the striking and struck vehicles directly determines how momentum is partitioned, making it the dominant factor in delta-V for the struck vehicle.

Question 3

In crash dynamics, 'restitution phase' refers to:

Accepted Answer

The period during which vehicles spring apart after reaching maximum crush

Answer

The restitution phase follows maximum engagement, during which stored elastic energy releases and the vehicles begin to separate.

Question 4

A vehicle traveling at 30 mph skids to a stop on dry asphalt with a drag factor of 0.75. Approximately how far does it skid before stopping?

Accepted Answer

80 ft

Answer

Using the skid formula d = S²/(30f): d = 30²/(30 × 0.75) = 900/22.5 = 40 ft.

Question 5

Which of the following best describes 'impulse' in the context of crash dynamics?

Accepted Answer

The product of force and the time over which it acts

Answer

Impulse equals force multiplied by the duration of its application (J = F×Δt), and by the impulse-momentum theorem, it equals the change in momentum.

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

ACTAR Crash Dynamics 3