Practice Test Geeks(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test
← All ACTAR Flashcard Decks

Crash Dynamics Flashcards

7 cards from real ACTAR practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

Read the first 7 Crash Dynamics flashcards as text

  1. During a head-on collision between two vehicles of equal mass and equal speed, what happens to their combined momentum?

    Answer: It equals zero

    When two equal-mass vehicles traveling at equal and opposite speeds collide head-on, their momenta cancel, resulting in a net combined momentum of zero.

  2. Which term describes the ratio of the relative separation speed to the relative approach speed of two colliding objects?

    Answer: Coefficient of restitution

    The coefficient of restitution (e) quantifies the elasticity of a collision by comparing post-impact separation speed to pre-impact approach speed.

  3. In crash reconstruction, the 'crush stiffness coefficient' (A and B) is used primarily to determine what?

    Answer: Delta-V from crush depth measurements

    The Campbell crush model uses empirically derived stiffness coefficients A and B to relate residual crush depth to the energy absorbed and estimate Delta-V.

  4. A vehicle strikes a fixed rigid barrier and comes to a complete stop. If the vehicle's mass is 1,500 kg and its pre-impact speed is 20 m/s, what is its initial kinetic energy?

    Answer: 300,000 J

    Kinetic energy = ½mv² = 0.5 × 1,500 × (20)² = 0.5 × 1,500 × 400 = 300,000 J.

  5. What is the primary reason vehicle roof crush is analyzed separately from frontal/side crush in ACTAR reconstructions?

    Answer: Roof crush involves different energy absorption mechanics and occupant space intrusion concerns

    Roof crush analysis focuses on structural intrusion affecting occupant survival space, governed by different stiffness characteristics than frontal or side impacts.

  6. During an oblique impact, the 'principal direction of force' (PDOF) is best described as:

    Answer: The direction in which the greatest crush force is applied to the vehicle

    PDOF is the direction along which the primary crush force acts on the vehicle during impact, which may differ from the vehicle's pre-impact heading.

  7. In a two-vehicle collision reconstruction, if Vehicle A's post-impact trajectory is known and Vehicle B's is known, conservation of momentum allows the reconstructionist to:

    Answer: Calculate pre-impact speed vectors for both vehicles

    By applying conservation of momentum with known post-impact velocities and directions, the reconstructionist can solve for the pre-impact speed vectors of both vehicles.