The Questions

April 13 - April 17, 1998

Question #1:

This week's Internet search question of the week pertains to the topic of traffic accident reconstruction. Traffic accident investigators use a long list of physics tricks to analyze an accident scene and to determine the pre-accident motion characteristics of the colliding vehicle(s). Of course, police, lawyers, and insurance companies all have an interest in the findings of the investigation. One of the key motion characteristics which investigators wish to determine is the pre-collision speeds of the vehicle(s). How fast was the vehicle moving prior to impact and to what certainty can this be determined? That is the question which is often asked of the traffic investigator in the courtroom and that is the question which you will ponder in this week's questions of the week.

Use a major search engine (HotBot, Lycos, Alta Vista, Excite, Dogpile, etc.) to find a site titled Summit Engineering. (If you still cannot find the page, you will likely find a link from a GBS page - visit the Project Corner, click Year-End Projects, click on the Physics of Automobile Collisions, click on a page full of WWW links, and look for the Summit Engineering link.) Summit Engineering is an engineering firm which conducts extensive accident investigations - one type being traffic accident investigations. From the home page, you will find a link to a page titled Speed Evaluation - Working With the Vehicle Accident Reconstructionist. Read the whole page (if you wish) but your question will focus on the short section titled Damage/Energy Analysis.

Once you have found and studied the Speed Evaluation page of the Summit Engineering site, do the following:

1. Identify the URL (address) of the page.
2. Describe the search path which you took to find the page (see example description).
1. Describe what damage analysis is and explain how it can be used to determine the pre-collision speed of a vehicle.
2. In your own words, describe the three difficulties with the process of damage analysis and why these difficulties limit the certainty of the findings from such an investigation.

Question #2:

In your physics question of the week, you will use the work-energy theorem and some sample data from a staged crash test and an actual accident to predict the pre-collision speed of a vehicle in an accident.
1. In a crash test, a '98 Corvette (m=1224 kg) moving at 20 mi/hr (2.24 mi/hr = 1 m/s) collided head-on with a wall. The Corvette came to a stop (obviously) and its front end was crumpled a distance of 0.37 m. Determine the force which acted upon the Corvette during the collision. PSAYW

2. In a typical drive through town, Dizzy Blonde failed to maneuver her '98 Corvette (m=1224 kg) out of the way of a parked car (which happended to be a Mercedes). Analysis of the accident scene (particularly, the final locations of the Mercedes within the parking space) revealsed an estimate of 1.8 m/s as the post-collision speed of the Corvette. Investigators estimated that the front end of the '98 Corvette was crumpled a distance of 0.42 m. Use the work-energy theorem and the information from the above crash test to determine the pre-collision speed of Dizzy's Corvette. PSAYW