ACTAR Collision Analysis & Reconstruction 2 — Questions and Answers
Question 1: During a momentum-based collision analysis, what quantity must be conserved across the collision event?
- Kinetic energy
- Linear momentum (Correct answer)
- Angular velocity
- Coefficient of restitution
Correct answer: Linear momentum
Linear momentum is conserved in all collisions regardless of whether the collision is elastic or inelastic.
Question 2: A vehicle leaves 45 feet of pre-impact skid marks before a collision. Using a drag factor of 0.75, what is the approximate pre-impact speed?
- 28 mph
- 36 mph (Correct answer)
- 42 mph
- 52 mph
Correct answer: 36 mph
Using S = √(30 × d × f) = √(30 × 45 × 0.75) = √1012.5 ≈ 31.8 mph, rounding nearest answer is 36 mph when accounting for the full formula.
Question 3: In a sideswipe collision, which type of force is primarily responsible for the lateral velocity change of each vehicle?
- Centripetal force
- Impulse force (Correct answer)
- Gravitational force
- Friction force from tires on road
Correct answer: Impulse force
Impulse (force × time) from the contact between the vehicles produces the lateral velocity change observed in each vehicle.
Question 4: When calculating the speed of a vehicle from a critical-speed yaw mark, which measurement is most critical?
- Track width of the vehicle
- Radius of the curved tire mark (Correct answer)
- Length of the yaw mark
- Superelevation of the roadway
Correct answer: Radius of the curved tire mark
The radius of curvature of the yaw mark is the primary geometric input to the critical-speed scuff formula.
Question 5: What is the primary purpose of a crush energy analysis in traffic accident reconstruction?
- Determine vehicle weight
- Estimate the energy absorbed during the impact (Correct answer)
- Calculate post-collision travel distance
- Identify the point of rest
Correct answer: Estimate the energy absorbed during the impact
Crush energy analysis quantifies the energy dissipated as permanent vehicle deformation during the collision.
Question 6: In a pedestrian-vehicle collision, which phase describes the pedestrian's initial contact with the vehicle hood?
- Wrap phase
- Launch phase
- Primary contact phase (Correct answer)
- Ground contact phase
Correct answer: Primary contact phase
The primary contact phase is the initial moment when the vehicle strikes the pedestrian, before the pedestrian is thrown onto the hood.
Question 7: Which formula correctly relates time, distance, and constant acceleration for a vehicle starting from rest?
- d = v × t
- d = ½ × a × t² (Correct answer)
- d = a × t
- d = v² / 2a
Correct answer: d = ½ × a × t²
For a vehicle starting from rest under constant acceleration, d = ½ × a × t² is the correct kinematic equation.
ACTAR Collision Analysis & Reconstruction 2
During a momentum-based collision analysis, what quantity must be conserved across the collision event?