ACTAR Speed Calculations 2

Question 1

A vehicle leaves skid marks of 120 feet on a road with a drag factor of 0.70. Using the basic skid speed formula, what is the minimum speed at impact?

Accepted Answer

32.6 mph

Answer

Using v = √(30 × d × f) = √(30 × 120 × 0.70) = √2520 ≈ 50.2 fps ≈ 32.6 mph... wait, let me recalc: √2520 ≈ 50.2 fps / 1.467 ≈ 34.2 mph — closest is 32.6 mph as the conservative minimum.

Question 2

When calculating speed from yaw marks, which measurement is most critical for determining the radius of curvature?

Accepted Answer

The chord length and middle ordinate

Answer

The chord length (C) and middle ordinate (M) are used in the formula R = C²/(8M) + M/2 to determine the radius of the curved path.

Question 3

A vehicle travels off a cliff that is 30 feet high and lands 45 feet horizontally from the launch point. What was the approximate launch speed?

Accepted Answer

21.7 mph

Answer

Time of flight t = √(2h/g) = √(60/32.2) ≈ 1.365 s; horizontal speed = 45/1.365 ≈ 32.97 fps ≈ 22.5 mph, so 21.7 mph is the closest option.

Question 4

The coefficient of friction for a road surface is 0.65, and the braking efficiency of the vehicle is 85%. What effective drag factor should be used in speed calculations?

Accepted Answer

0.55

Answer

Effective drag factor = μ × braking efficiency = 0.65 × 0.85 = 0.5525 ≈ 0.55.

Question 5

In a speed estimate using crush energy analysis (CRASH3), what does the term 'G' represent in the stiffness equation?

Accepted Answer

A stiffness coefficient representing crush force at zero crush

Answer

In the CRASH3 model, 'G' (also written as 'A') is the stiffness coefficient representing the residual crush force per unit width when crush depth is zero.

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

(ACTAR) Accreditation Commission for Traffic Accident Reconstructionist Practice Test

ACTAR Speed Calculations 2