Miscellaneous Questions
from January
2002 Newsletter
(1) A vector is a quantity which has both magnitude
and _______________.
Answer: Direction. Scalar quantities are like points
on a SCALE and vector quantities are scalar quantities that also have a
specific directional component. For example, simply stating "the car's
going 35 mph," we know the car's going SOMEwhere at 35 mph, but all
we've actually described is the the magnitude of the speed and speed, by
itself is scalar quantity. If we say, "the car's going 35 mph eastbound"
then we not only have a description of the magnitude of the speed by the
direction of that speed and have described a vector.
(2) When working with vector diagrams, the length of a given
vector line times the scale of the diagram is equal to...
a. the velocity of one vehicle or another
b. the angle of the vector
c. the magnitude of the vector
d. none of the above
Answer: (c) The MAGNITUDE of the vector . Typically,
when drawing a vector diagram as part of a momentum analysis, individual
vectors are represented in the drawing after multiplying the vehicle's mass
times its velocity (its momentum) and then drawing a line at a specific
angle or heading at the scale of the drawing. Magnitude, in this case, means
length. For example, without respect to particular units of momentum, if
we have a mass times a velocity and the total momentum is 300,000 (units)
and we are constructing a vector diagram at a scale of 1inch =20,000 units
then the length of that vector we'd have to draw would be 15 inches (300,000/20,000=15)
at a specified angle. So, if we have a length of a given vector measured
at 12 inches and the scale of 1in=30,000 multiplying 12 by 30,000 gives
us 360,000 (units).
(3) True or False, the Flight Data Recorder (FDR), Cockpit
Voice Recorder (CVR), the automobile Sensing Diagnostic Module (SDM) and
the automobile Event Data Recorder (EDR) all share a common primary function.
Answer: False. While the ground transportation Event
Data Recorder (EDR) is similar to the aviation data recorder systems, the
Sensing Diagnostic Module (SDM) - in which the EDR is located - has a distinctly
different primary function. The FDR, EDR and CVR all share a primary function:
event information collection. These systems don't control any functions
of the vehicle. The SDM; however, while it does contain the ground transportation
EDR, has a different primary function. The SDM's primary functions are to
analyze (diagnostic) the motor vehicle's air bag system and then power the
system up such that when it senses a crash, its internal algorithm can evaluate
the anticipated severity and either deploy the air bags or not depending
on the individual event. So, the SDM has, as its primary function, system
control features whereas the data recorders (the EDR, CVR and FDR) are not
control units but, in a sense, responding units.
Depositions: Part 1
from November
2001 Newsletter
Question: What is a "Stipulation"?
Answer: A stipulation is an agreement
between counsel regarding facts or procedure. In many jurisdictions counsel
will start the deposition and agree to the "usual" or "standard"
stipulations.
Example:
Cousel A: Stipulations?
Counsel B: She would like to waive the reading and signing.
Expert: I would like to read and sign the deposition, sir.
Counsel B: Sorry. The witness reserves the right to read and sign
the deposition transcript within 30 days of receipt of said transcript.
Lesson:
You generally have a right to read and sign your deposition. You shouldn't
let counsel waive that right unless you want to.
Question: What is an "Objection"?
Answer: Rule 30 of the Federal Rules of
Civil Procedure: "(1) Any objection to evidence during a deposition
shall be stated concisely and in a non-argumentative and non-suggestive
manner. A party may instruct a deponent not to answer only when necessary
to preserve a privilege, to enforce a limitation on evidence directed by
the court, or to present a motion under paragraph (3)."
What this means as a practical matter is that
the standard objections covered by counsel may include:
- form of question (e.g., leading the witness)
- competency
- relevancy
- materiality, and
- nonresponsive answer
Your role as an expert is not to argue evidence or procedure.
You are NOT an advocate and will lose credibility if you appear to be one.
With this in mind, it is recommended that you do the following when an objection
is made:
- Stop testifying immediately
- Listen carefully to the objection
- learn as much as you can about the grounds for the objection
- Let the lawyers battle it out between themselves
- Resume testifying when counsel so instructs you
Question: What is meant by "Instructions Not to
Answer"?
Answer: Under the Federal Rules, an attorney may only
instruct a deponent not to answer to preserve a privilege, to enforce a
limitation of evidence directed by the court, or to preserve a motion that
the deposition is being "conducted in bad faith or in such a manner
as unreasonably to annoy, embarrass, or oppress." Ultimately, the legitimacy
of any instruction not to answer may be evaluated by the court.
Answers to these questions were taken from "How
To Excel During Depositions: Techniques for Experts That Work".
Conservation of Momentum & Dissipation
of Energy
from June
2001 Newsletter
The variables:
S1 = Speed of V-1 at impact
s1 = Speed of V-1 after impact = 0 mph
S2 = Speed of V-2 at impact, reportedly 50 mph
s2 = Speed of V-2 after impact = 0 mph
ebs1 = equivalent barrier speed of V-1 from crush
ebs2 = equivalent barrier speed of V-2 from crush
W1 = Weight of V-1 = 2734 + 245 + 150 = 3135 lb.
W2 = Weight of V-2 = 3175 + 210 + 30 = 3415 lb.
Weight Ratios: If W1 = 1, W2
= 3415/3129 = 1.089
CALCULATION ONE:
Substituting into the conservation of momentum formula:
S1*W1 + S2*W2
= s1*W1 + s2*W2
S1*1 + -50*1.089 = 0*1 + 0*1.089
S1 = 54.45 or 54 mph [88 kmh]
CALCULATION TWO:
We must estimate the energies absorbed by crush via determination of their
equivalent barrier impact speeds.
Average crush to the front of V-1:
CAVE = (34.5+35.5+36+36+36+33.5)/6
= 35.25 inches
Crush energy equivalent barrier speed:
ebs1 = 1.25*CAVE + 7 =
1.25*35.25 + 7 = 51.1 mph
Average crush to the front of V-2:
CAVE = (32.5+33.5+34+34.5+34+32.5)/6
= 33.5 inches
Crush energy equivalent barrier speed:
ebs2 = 1.25*CAVE + 7 =
1.25*33.5 + 7 = 48.9 mph
Substituting into the dissipation of energy
equation:
S12*W1 + S22*W2
= s12*W1 + s22*W2
+ ebs12*W1 + ebs22*W2
S12*1 + 502*1.089
= 02*1 + 02*1.089 + 51.12*1+ 48.92*1.089
S12 + 2722 = 0 + 0 + 2611
+ 2604
S12 = 2493
S1 = 49.9 of 50 mph [80 kmh]
CALCULATION THREE:
We must solve for both speeds using momentum and energy.
Substituting into the conservation of momentum formula:
S1*W1 + S2*W2
= s1*W1 + s2*W2
S1*1 + -S2*1.089 = 0*1 + 0*1.089
S1 = 1.089*S2
Substituting into the dissipation of energy
equation:
S12*W1 + S22*W2
= s12*W1 + s22*W2
+ ebs12*W1 + ebs22*W2
S12*1 + S22*1.089
= 02*1 + 02*1.089 + 51.12*1+ 48.92*1.089
S12 + S22*1.089
= 0 + 0 + 2611 + 2604 = 5215
(1.089*S2)2 + S22*1.089
= 5215
2.275*S22 = 5215
S2 = 47.8 or 48 mph [77 kmh]
S1 = 1.089*S2 = 52.14
or 52 mph [84 kmh]
At-Scene Investigation
from April 2001 Newsletter
- Three reasons why police departments need to prepare
for traffic accident investigation are:
- Many other agencies and individuals depend on police
to conduct at least the __________ investigation.
- Accident investigation is important to traffic _____________
enforcement.
- Inept investigation can squander valuable police
resources.
- Five data areas where supplemental forms are useful
to produce additional data on special aspects of accidents are injuries
to persons, tire disablement, collapse in collisions, safety-belt usage,
and singular-vehicle accidents. True or False?
- Traffic accident forms easily accomodate narrative
and argumentative information. True or False?
- Forms for traffic accident data collection have limitations,
because they stifle further _____________, are inadequate for questioning
a driver involved in an accident, and discourage _______________ of unusual
circumstances and precise descriptions.
- For most minor accidents that do not involve significant
injuries, towed vehicles, or witnesses in addition to the people involved,
a simplified report form can be submitted by drivers if police do not
attend the accident. True or False?
- Filing accident report forms by ______________, rather
than by number, date or name, is generally recommended, primarily because
people remember where an accident happened.
- Photographs are an _________________, permanent record
of observations that record details in investigator may fail to note.
- A single lens reflex camera with an f/2.8 or better
lens, a 1/125 shutter speed, and a normal focal length, used with 35 mm
color film, is recommended for traffic accident photos. True or False?
- Planning at-scene investigations involves decisions
about what _______________ be done, what ______________ be done, and what
_________________ be done.
- Five times during investigation at the scene, the
situation can be evaluated well enough to plan what to do next. These
stages of planning are:
- on learning of the accident
- on _______________ at the scene
- when the emergency is under __________________
- when urgent data collection is ______________________
- when work at the scene is finished.
Answers
- at-scene, law
- True
- False; not enough blank space
- inquiry, recording
- True
- location
- indisputable
- True
- must, should, might
- arrival, control, complete
Projectile Motion
from March 2001 Newsletter
Q1. A vehicle failed to negotiate a curve
in the roadway, ran off of the highway and became airborne. We document
the collision scene and determine that the center of mass of the vehicle
traveled 59 feet horizontally and fell 11 feet vertically. The launch path
was level. Determine the launch speed.
Q2. Use the data from question 1, but consider
the case where the grade of the launch path is measured at 0.10. Determine
the launch velocity.
Q3. Use the data from question 1, but consider
the case where the grade of the launch path is measured at -0.10. Determine
the launch velocity.
Following is the equation we will use for
determining the velocity of the vehicle at launch:
 |
= initial velocity (at launch) |
 |
= approximately 32.2 feet per second squared,
acceleration from gravity |
 |
= launch angle (+/-) |
| x |
= difference in altitude from launch point
(+/-) |
| y |
= horizontal distance traveled |
Answer Q1
= approx. 71.37 feet per second or approx.
48 miles per hour
Answer Q2
We are given the grade of 0.10, by definition
the grade is the ratio of rise or fall to horizontal distance, this ratio
equals the tangent of angle .
So we need to find the angle whose tan is 0.10.
= approx. 57.87 feet per second or approx.
39 miles per hour
Answer Q3
= approx. 105.34 feet per second or approx. 71 miles
per hour
Note that in examples 1 through 3,
"g" is substitued as 32.2 feet per second squared, a negative
sign is already in front of the variable, changing the value to -32.2 feet
per second squared. The reason for this is that the acceleration is in the
negative direction in the chosen frame of reference. The launch angle (alpha)
must be substituted as a positive or negative number. It can be approximated
by measuring the grade and using the inverse tangent function to find the
angle having that value as its tangent. Alpha may be used in any desired
units provided that consistency is employed throughout. "x" and
"y" values are normally listed in feet, although the units may
vary depending on the application, consistency is the key, along with a
unit analysis. "y" values are listed as positive or negative numbers
depending on whether the touchdown point is higher (+) or lower (-) than
the launch point.
These practice problems were taken from
"Basic Collision Analysis and Scene Documentation" by David A.
Casteel and Steven Moss.
If you wish to order their book, please click
here.
Photogrammetry
from January 2001 Newsletter
These questions are either TRUE or FALSE
- The mapmaker usually has complete and accurate measurements
to begin with, because of the knowledge, skill, equipment, time and motivation
of investigators.
- Photographs are a valuable source (sometimes the
only source) of data for an after-situation map.
- The common idea of photogrammetry is aerial mapping
in which a photo is taken straight down from an aircraft, resulting in
an orthogonal (perpendicular) view.
- Changing a perspective view in an ordinary photograph
to an orthogonal view required for mapping can be done graphically by
drawing, but not mathematically by calculation.
- A good way to compare your map with a photograph
is to view the map from about the same low angle that the camera height
produced when the picture was taken.
- If all or part of a map has been drawn from photos,
it is a good idea to explain this in a note on the map.
- A line in a photo is represented on the corresponding
map by several points along that line; if the line is straight, only the
ends need to be located, because a straight line in a photo perspective
is always a straight line on the map.
- A perspective grid map is noticeably affected by the type
of camera and focal length of the lens used to take the pictures.
Answers
- FALSE: such data is rarely available at this
point
- TRUE
- TRUE
- FALSE: by math calculation also
- TRUE
- TRUE
- TRUE
- FALSE: NOT noticeably affected
Estimating Vehicle Stopping Distances
from November 2000 Newsletter
These questions are either TRUE or FALSE
- A vehicle is considered as fully sliding unless
there are definite signs that it was rotating or swerving, or that some
brakes were not functioning?
- If all wheels make marks, use the average length
of the marks for your "stopping distance" figure?
- The drag factor is the coefficient of friction between
tires and road on a level surface with all wheels sliding?
- Test skids can be impractical and dangerous, and
often give too little drag factor because brakes are not applied quickly
enough or strongly enough to lock all wheels instantly?
- Lacking proper test skids, approximate drag factors
may be used?
- Driver reaction time for a simple reaction (when
a driver has decided in advance what to do if something expected happens)
is short; .20 to .30 of a second for most people?
- Discriminative reaction (when a driver has to seek additional
information to decide what to do) requires the most time - from a second
to a minute or more?
Answers
- TRUE
- FALSE; You should use the length of the longest
mark
- TRUE
- FALSE; They often give too GREAT a drag factor
- TRUE
- TRUE
- TRUE
Tires and Tire Safety
from October 2000 Newsletter
These questions are True or False
- There are three basic types of tires used on highways
today: radial tires, bias belted tires, and bias tires?
- Most police accident investigators have the ability
to determine whether tire failure was due to abuse, misapplication or
defect?
- No information is molded on tires during the retreading
process?
- The bias tire has its body plies run from bead to
bead in a bias or somewhat diagonal direction, and the plies generally
alternate in direction?
- A tire failure may well result from a malfunction
of one of the other components of the vehicle suspension system - brakes,
linkages, springs, spindles, etc.?
- There is no disadvantage in removing a damaged tire-wheel
assembly from the scene for later tire examination?
- Heat deterioration may be considered in four general
categories: 1) heavy burn, 2)scorching, 3) heat generation, and 4) tread
friction?
- Depth of an abnormality can be described in one of
three categories: 1) superficial (no plies or bead wires are exposed),
2) penetration (plies or bead wires are exposed), and 3) through (damage
extends from outside to inside)?
- A condition where one or more of the laminate components
(layers) of the tire has come apart is called lamination?
- A stopped wheel can be indicated by localized flange
abrasion or by striations perpendicular to direction of tire movement?
- Sideslipping wheels are indicated by transverse striations
on sidewalls and sometimes on treads?
TRUE.
- Photos are rarely needed if the tire itself can be retained
for future reference?
TRUE.
Answers
- TRUE
- FALSE; special training is required
- FALSE; information is molded on retreads
- TRUE
- TRUE
- FALSE; there are many possible disadvantages
- TRUE
- TRUE
- FALSE; called separation
- FALSE; parallel to direction of tire movement
- TRUE
- TRUE
Lamp Examinations
from September 2000 Newsletter
These questions are True or False.
- Brittle fracture occurs with vibration or impact
in a hot filament.
- A third filament is used in some headlights to give
a glow in the lamp if the main filament burns out.
- Halogen lamps, after a crash, are more likely to
indicate on or off than ordinary sealed-beam headlamps.
- Oxide smoke, consisting of oxides of tungsten that
rise rapidly from an exposed incandescent filament, leaves a whitish dust
on nearby surfaces - a tell-tale sign that there was an incandescent filament
in the lamp after the glass broke.
- The turn flasher and the brake (steady) signals are usually
in the same filament in REAR lamps. If the investigator determined that
the lamp was ON, he could not tell whether the brake signal, the turn
signal, or both were operating.
Answers
- FALSE. Brittle fracture occurs with vibration
or impact in a COLD filament.
- TRUE. A third filament is used in some headlights
to give a glow in the lamp if the main filament burns out.
- FALSE. Halogen lamps, after a crash, are LESS
LIKELY to indicate on or off than ordinary sealed-beam headlamps.
- TRUE. Oxide smoke, consisting of oxides of
tungsten that rise rapidly from an exposed incandescent filament, leaves
a whitish dust on nearby surfaces - a tell-tale sign that there was an
incandescent filament in the lamp after the glass broke.
- TRUE. The turn flasher and the brake (steady) signals
are usually in the same filament in REAR lamps. If the investigator determined
that the lamp was ON, he could not tell whether the brake signal, the
turn signal, or both were operating.
Vaults & Estimating Impact Speeds
from May 2000 Newsletter
- An auto slides sideways into a curb and becomes airborne.
The horizontal distance of the vault is 56 feet. The drop in elevation
is 3 feet 6 inches. Determine the minimum take-off speed.
SOLUTION:
The solution of this problem is a simple matter of applying the vault
formula. (This equation assumes a 45 degree take-off angle which, in
cases involving little or no change in elevation from take-off to landing,
yields the most conservative speed needed for the vehicle to make the
flight.)
S = Speed of the vehicle in mph
d = horizontal flight distance (56 feet)
H = change in height (-(3 + 6/12) = -3.5' downward)
Now substitute these values into the equation and solve:
S = 28.1 or 28 mph [45 khm]
- A sports car is attempting to pass a truck when the
sports car collides head-on with another vehicle. The sports car, which
was found in third gear, had a 4-speed transmission. Examination of the
tachometer reveals a needle "whip" mark at 3400 rpm. Given that the sports
car has a transmission ratio (3rd gear) of 1.00, an axle ratio of 3.25,
and a drive wheel diameter of 23 inches, use the needle mark to estimate
the impact speed of the sports car.
SOLUTION:
To solve this problem we need the following information:
The engine crankshaft speed in revolutions per minute, RPM, the transmission
(gear) ratio, the number of times the engine crankshaft will turn for
every for every time the driveshaft turns, iT, the axle ratio,
the number of times the driveshaft will turn for every time the axle
shaft turns, iA, and the radius of the drive wheels
Given that there are two times pi (3.1416) inches of
circumference for every inch of a tire's radius, times 60 minutes in
every hour, divided by 12 inches in every foot and divided by 5280 feet
in every mile, leaves us with a conversion constant of 0.00595. Therefore
our equation is:
Where:
S = Speed of the vehicle in mph
RPM = Engine crankshaft speed = 3400 revs/min
R = Radius of the tire = 23/2 = 11.5 inches
iT = Gear ratio = 1.00
iA = Axle ratio = 3.25
= 71.58 or 72 mph [115 kmh]
Determining Speeds
from April 2000 Newsletter
- A vehicle left inertial scuffmarks on a curve with
10% superelevation. Using a 50-foot chord, you measure a 12-inch middle
ordinate. µ on a flat curve would be 0.60. Determine the vehicle's speed
from this information.
- A vehicle left inertial scuffmarks on a curve with
8% superelevation. Using a 25-foot chord, you measure an 8-inch middle
ordinate. µ on a flat curve would be 0.75. Determine the vehicle's speed
from this information.
Q1: ANSWER: 83.99 FPS or 57 MPH
SOLUTION:
c = 50 feet (given)
m = 1 foot (given 12 inches, convert to feet)
R = 313 (solved below)
u = 0.70 (0.60 + 0.10 for superelevation)
Q2: ANSWER: 56.07 FPS or 38 MPH
SOLUTION:
c = 25 feet (given)
m = .67 feet (given 8 inches, convert to feet)
R = 117.64 (solved below)
u = 0.83 (0.75 + 0.08 for superelevation)
Determining Speeds
from February 2000 Newsletter
- A vehicle skids 16 feet into a parked car on a roadway
where µ = 0.81. From post-collision movement you are able to determine
an impact velocity of approximately 60 FPS. What was the vehicle's velocity
at the start of the skid?
ANSWER: 66.2 FPS or 45 MPH
- A vehicle skids to a stop in a distance of 193 feet.
The first 23 feet are on asphaltic-concrete (µ = 0.80), the following
51 feet are on a dirt surface (µ = 0.51) and the final 119 feet are on
a grass field (µ = 0.37). Determine the vehicle's velocity at the start
of the skid. Was the driver exceeding the posted 35 MPH speed limit?
ANSWER: 75.47 FPS or 51 MPH. YES, the driver
was exceeding the posted speed limit.
