ACTAR Mathematical & Physical Principles of Reconstruction 4

Question 1

A 3,600-lb vehicle traveling at 60 mph collides with a stationary 2,400-lb vehicle, and they move together post-impact. What is the combined post-impact speed (use 88 ft/s for 60 mph)?

Accepted Answer

36.0 mph

Answer

COLM: m1v1 = (m1+m2)v2; v2 = (3600 × 88)/(3600+2400) = 316,800/6000 = 52.8 ft/s ≈ 36 mph.

Question 2

The equation for stopping distance on a grade where θ is the road angle is S = v²/[2g(f ± sin θ)]. The ± accounts for:

Accepted Answer

Uphill adding to braking, downhill reducing braking effectiveness

Answer

On a downgrade, gravity assists motion and reduces effective braking (minus); on an upgrade, gravity opposes motion and aids braking (plus).

Question 3

Impulse is defined as the product of:

Accepted Answer

Force and time

Answer

Impulse J = F × Δt, and by the impulse-momentum theorem, impulse equals the change in momentum (J = Δp).

Question 4

In a rollover event, the vehicle's center of gravity height (hcg) and track width (T) determine the static stability factor (SSF). Which formula is correct?

Accepted Answer

SSF = T / (2 × hcg)

Answer

SSF = T/(2hcg); a higher SSF (wide track, low CG) indicates greater resistance to rollover.

Question 5

A vehicle in a 90° turn at constant speed experiences which type of acceleration?

Accepted Answer

Centripetal (centrifugal) acceleration directed toward the center of curvature

Answer

Even at constant speed, circular motion requires centripetal acceleration directed toward the center of the curve to continuously change the velocity direction.

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

ACTAR Mathematical & Physical Principles of Reconstruction 4