| Topic: |
Science > Physics |
| User: |
"gianluca" |
| Date: |
15 Mar 2005 11:35:15 AM |
| Object: |
A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
Well, here is the problem:
a pedestrian is hit by a car and jumps away to a fixed distance X.
:shock:
Knowing the value of the mass of both pedestrian and car (Mp and Mc
respectively, in kg), find out the speed at which the car did hit the
pedestrian.
:?:
Thanks in advance for the help. 8)
Gianluca
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| User: "gianluca" |
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| Title: re:A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
24 Mar 2005 03:35:22 AM |
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Any other suggestion? :idea:
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| User: "gianluca" |
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| Title: re:A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
17 Mar 2005 11:34:36 AM |
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Pete, do you have a rough idea of how far the boy flew away when you
hit him?
Provided that obviously the geometry of the car is fundamental.
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| User: "bz" |
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| Title: re:A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
17 Mar 2005 12:18:35 PM |
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gcuomo@unibas-dot-it.no-spam.invalid (gianluca) wrote in news:4239bfac$1_2@
127.0.0.1:
Pete, do you have a rough idea of how far the boy flew away when you
hit him?
Provided that obviously the geometry of the car is fundamental.
I suspect you have been trolled.
--
bz
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+sp@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
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| User: "pete" |
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| Title: Re: A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
17 Mar 2005 03:04:52 PM |
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gianluca wrote:
Pete, do you have a rough idea of how far the boy flew away when you
hit him?
It was a long time ago, but I think the car skidded about
30 feet and then he flew about 15 feet, maybe 20.
--
pete
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| User: "gianluca" |
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| Title: re:A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
16 Mar 2005 05:34:29 AM |
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Well, shortly:
-I have not started any analysis yet, since I do not know where to
start from ..
- unfortunately the pedestrian died in the collision.
- he was found some 30 metres away from the impact point;
- the speed limit was 50 km/h;
- the friction coefficient of asphalt is known;
- density and temperature of air are known;
- any sort of assumption simulating real situations can be made;
- the car characteristics are known .
Please help me, since I have to provide important info about a person
who was killed in the accident.
Thanks
Gianluca
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| User: "bz" |
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| Title: re:A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
16 Mar 2005 06:45:46 AM |
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gcuomo@unibas-dot-it.no-spam.invalid (gianluca) wrote in news:423819c5$1_1@
127.0.0.1:
Well, shortly:
-I have not started any analysis yet, since I do not know where to
start from ..
- unfortunately the pedestrian died in the collision.
- he was found some 30 metres away from the impact point;
- the speed limit was 50 km/h;
- the friction coefficient of asphalt is known;
- density and temperature of air are known;
- any sort of assumption simulating real situations can be made;
- the car characteristics are known .
Please help me, since I have to provide important info about a person
who was killed in the accident.
Thanks
Gianluca
Free advice: this sounds like a job for someone with skills in physics,
good credentials, an ability to look good on the witness stand and good
Errors and Omissions Insurance. In other words, I suggest you hire a
professional.
You want to make sure that the anwers you get are correct. Here, one can
never tell who is proposing an answer nor how valid it is. You may get the
right answer, you will certainly get some wrong ones.
- he was found some 30 metres away from the impact point;
His mass? His 'angle of launch' might be deducable from damage to the car
and damage to his body.
- the speed limit was 50 km/h;
Was the car going the limit, over the limit, under the limit? Do you know?
- the friction coefficient of asphalt is known;
Were there skid marks? If not, the friction coefficient is probably not
needed.
- density and temperature of air are known;
Probably had little influence on his trajectory. The transfer of momentum
from the car to his body would have been much more important. How much
went into deformation and how much went into Kinetic Energy/velocity.
- any sort of assumption simulating real situations can be made;
Assumptions are not reality. Garbage in -- garbage out. Do you want correct
answers or only possible answers?
- the car characteristics are known .
That will help, along with the damage done to the car and body.
--
bz
please pardon my infinite ignorance, the set-of-things-I-do-not-know is an
infinite set.
bz+sp@ch100-5.chem.lsu.edu remove ch100-5 to avoid spam trap
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| User: "tadchem" |
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| Title: Re: A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
15 Mar 2005 12:53:30 PM |
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gianluca wrote:
Well, here is the problem:
a pedestrian is hit by a car and jumps away to a fixed distance X.
:shock:
That *is* a shock.
It is also a trick question.
When a pedestrian is *hit* by a car, the immediate effect is fractures
to the tibia and fibula in one or both legs, making "jumping"
impossible.
How far the poor sap would be launched would depend on a lot of
information that hasn't been provided - angles, heights of barycenters
and impact point, various coefficients of friction, obstacles, and of
course the predilictions of the witnesses.
Tom Davidson
Richmond, VA
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| User: "pete" |
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| Title: Re: A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
17 Mar 2005 05:59:46 AM |
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tadchem wrote:
gianluca wrote:
Well, here is the problem:
a pedestrian is hit by a car and jumps away to a fixed distance X.
:shock:
That *is* a shock.
It is also a trick question.
When a pedestrian is *hit* by a car, the immediate effect is fractures
to the tibia and fibula in one or both legs, making "jumping"
impossible.
How far the poor sap would be launched would depend on a lot of
information that hasn't been provided - angles, heights of barycenters
and impact point, various coefficients of friction, obstacles, and of
course the predilictions of the witnesses.
The pedestrian: an fat 10 year boy.
The car: a 1968 Chrysler New Yorker, 4600 lbs.
When I did it at 40 mph,
the pedestrian rolled up the hood onto the windshield
and wasn't launched until the car came to a screaching halt,
which made me wonder if he would have been better off
if I had slowed down slowly after hitting him,
instead of slamming on the brakes. He went flying far.
--
pete
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| User: "tadchem" |
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| Title: Re: A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
17 Mar 2005 08:41:42 AM |
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Having once witnessed a pedestrian (a 12 year old boy) getting smeared
across the front of a minivan, I can assure all that the geometry of
the vehicle is a significant factor.
Tom Davidson
Richmond, VA
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| User: "Sam Wormley" |
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| Title: Re: A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
15 Mar 2005 12:01:02 PM |
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gianluca wrote:
Well, here is the problem:
a pedestrian is hit by a car and jumps away to a fixed distance X.
:shock:
Knowing the value of the mass of both pedestrian and car (Mp and Mc
respectively, in kg), find out the speed at which the car did hit the
pedestrian.
Show us what you've done so far.
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| User: "gianluca" |
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| Title: re:A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
18 Mar 2005 05:34:03 AM |
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ok, thanks pete
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| User: "gianluca" |
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| Title: re:A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
16 Mar 2005 05:34:29 AM |
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tadchem ... obviuosly the verb "jump" was probably not appropriate,
since it is not a real jump: you would have probably used the verb
"fling".
The guy was killed, so he did not have the chance to jump...
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| User: "tadchem" |
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| Title: Re: A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
16 Mar 2005 10:25:34 AM |
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gianluca wrote:
tadchem ... obviuosly the verb "jump" was probably not appropriate,
Given that your native language is not English, I can forgive the use
of the wrong verb.
First allow me to express my regrets that this is not a hypothetical
problem.
There are many possible and even likely considerations to be made.
(1) The victim may have been carried by momentum beyond the point where
the body landed - rolling or sliding.
(2) The victim may have moved under his own power after impact (unless
unconsciousness was instantaneous).
(3) The vehicle may have dragged the victim away from the impact point.
(4) There may be inaccuracies in determining the exact point of impact.
Briefly, there are too many unknown variables to reliably determine the
speed of the vehicle at impact.
IMO, your best option would be to consult with experts in traffic
safety to determine from *their* extensive experience how fast a
vehicle must have been moving if it was able to produce the results
observed.
Advanced Google
http://www.google.com/advanced_search?hl=en
search on *all* the words:
impact car distance pedestrian
If you have the time...
"Comprehensive Analysis Method for Vehicle/Pedestrian Collisions." SAE
#2000-01-0846.
<http://www.sae.org/servlets/productDetail?PROD_TYP=PAPER&PROD_CD=2000-01-0846>
A comprehensive method for assessing the vehicle impact speed in a
vehicle/pedestrian collision was derived. Mathematical models, real
world collision data and staged impact test data were referenced from
over sixty studies pertaining to pedestrian collisions. A practical
analytical approach for evaluating vehicle impact speed from the
post-impact vehicle damage, pedestrian injuries and pedestrian throw
distance was developed. $10.00
Tom Davidson
Richmond, VA
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| User: "gianluca" |
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| Title: re:A PEDESTRIAN IS HIT BY A CAR ... PROBLEM... |
16 Mar 2005 09:35:07 AM |
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the mass of the pedestrian is known.
the angle of "launch" can be deducted from the car - inclination of
hood and windshield.
the velocity of the car is not known, and this is basically the main
concern.
It was pedestrian's fault, but we are trying to understand if the car
broke the speed limit or not: i do not actually need to know exactly
the speed, but just to understand if it was over 50 km/h or not.
The car did not brake at all, therefore there are no signs on the
asphalt pavement.
i know it is hard job, but any suggestions of physics rules to be
applied are more than welcome.
Gianluca
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