ACTAR Crash Dynamics 5

Question 1

During a collinear rear-end collision (both vehicles traveling in the same direction), which formula correctly represents the conservation of momentum?

Accepted Answer

m₁v₁ + m₂v₂ = m₁v₁' + m₂v₂'

Answer

Conservation of momentum requires that the total momentum before impact equals total momentum after: m₁v₁ + m₂v₂ = m₁v₁' + m₂v₂' (with consistent sign convention).

Question 2

Which crash phase is characterized by the vehicles moving together at a common velocity, immediately before they begin to separate?

Accepted Answer

Maximum engagement (common velocity) point

Answer

At the point of maximum engagement, both vehicles momentarily share a common velocity before elastic recovery forces cause separation in the restitution phase.

Question 3

A vehicle with a center of gravity height of 0.6 m and a track width of 1.8 m is cornering. The approximate lateral acceleration threshold at which tip-over begins is approximately:

Accepted Answer

1.50 g

Answer

The static rollover threshold ≈ track width / (2 × CG height) = 1.8 / (2 × 0.6) = 1.5 g; below this, the vehicle slides before tipping.

Question 4

When two vehicles of different masses collide and stick together (perfectly plastic collision), post-impact velocity is calculated using:

Accepted Answer

(m₁v₁ + m₂v₂) / (m₁ + m₂)

Answer

In a perfectly plastic (inelastic) collision where objects stick together, the common post-impact velocity = total pre-impact momentum divided by total mass.

Question 5

An analyst finds that a vehicle's tires left yaw marks before impact. The primary information yaw marks provide for reconstruction is:

Accepted Answer

The minimum speed of the vehicle at the start of the yaw, via critical curve speed analysis

Answer

Yaw mark radius, combined with the road's friction coefficient, allows calculation of the minimum critical curve speed using the formula v = √(f × g × r).

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

ACTAR Crash Dynamics 5