Chapter 12 Algebraic Equations
Hit and Run
Overview: You are a forensic scientist and you will be preparing a court report of your investigation of a Hit and Run accident.
You will need to prepare a PowerPoint educating the jury on how you figure out acceleration and velocity. You will also need to reconstruct the incident and show mathematically how each of the suspects is either innocent or guilty. Your report should include both written and mathematical information. It should also include your data and graphs that you have developed by reconstructing the incidents.
Rania Sallum, 58, was struck by a large, dark-colored SUV Wednesday around 7:20 a.m. Sallum could not see the driver or read the license plate, but she knows that she was struck by
the front right bumper of the vehicle, which then slowed almost to a stop before speeding off.
She estimates that the incident occurred between 7:15 and 7:25 a.m. A hit-and-run bulletin and
vehicle description went out to all officers. Three police teams spotted vehicles with front right
bumper damage and recorded the following information from their drivers:
Suspect: Natalya Ludnova, 25--pulled over for speeding when the officer noticed bumper damage—claimed that damage was due to hitting the curb while parking.
Suspect: Everett Smalls, 38--brought in for blocking a fire lane—claimed that bumper was damaged in a stop-and-go rush hour fender bender.
Suspect: Antonia Angeles, 53--pulled over for speeding when the officer noticed bumper damage—claimed a neighbor backed into her car as she drove past his driveway.
EDR data downloaded from each car for the 10 seconds before and after the bumper collision show that each occurred between 7 and 8 a.m. Wednesday. See below.
Vernier Motion Detector
Vernier computer interface
toy car, at least 5 cm tall
1. Prepare the Motion Detector for data collection.
a. Connect the Motion Detector to the DIG/SONIC 1 channel of the interface.
b. Open the pivoting head. If the Motion Detector has a sensitivity switch, set it to Track.
c. Prepare the computer for data collection by opening the file “12 Hit and Run” from the Forensics with Vernier folder of Logger Pro.
2. Place the Motion Detector and car on a lab table or the floor. The Motion Detector should be facing the car, and they should be about 30 cm apart. Remove any surrounding objects so that the data you acquire will be relatively “noise” free.
3. Perform a test run with your car. Have one team member push the car and release it. Have another team member check the readings on the screen. You do not need to record the motion at this point. Just be sure that the Motion Detector is measuring the increasing distance as the car moves away. Also be sure that the car is pushed gently enough that it stops before the end of the table.
4. Position the team members so that one can start data collection and the other can push the car away from the Motion Detector.
5. Click COLLECT and push the car away after data collection begins. Be sure to push the car away in the same manner that you did in your test run.
6. Examine the distance and velocity graphs. These graphs should be relatively smooth,indicating that you picked up the motion of the car and not other objects. If the graphs of the distance and velocity are not relatively smooth (an absolutely smooth graph is rarely observed), repeat Step 5.
7. Sketch these graphs in the Evidence Record. Then complete the Case Analysis.
1. Look at the velocity vs. time graph. At what time did the car begin to move?
2. What was the maximum velocity of the car?
3. At what time did the car reach its maximum velocity?
4. Look at the distance vs. time graph. Does the time at which the car’s distance from the
Motion Detector increased match the time in question 1?
5. How far did the car move before it reached its maximum velocity?
6. EDRs in vehicles record information on velocity and acceleration for moving vehicles. The data recorded by EDRs help reconstruct the events of an accident. For example, data from the EDR can show when a car’s brakes were applied, if at all. Suppose a vehicle were traveling at a constant speed, using cruise control, when suddenly the brakes were applied until the vehicle stopped. Sketch a velocity vs. time graph for this situation. Label the point at which the brakes were applied and the point at which the vehicle came to a complete stop.
7. Do the EDR data taken from the suspects support their stories? Do the EDR graphs suggest that any of these suspects is the culprit in the hit and run? Explain your answers.
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