Car Collision Forensics Lab

A traffic accident occurred in a 35 km/hr
speed limit zone on Millway Street in which
a 3000-kg Cadillac Escalade SUV rearended a 2000-kg Subaru Outback Wagon
that was stopped at a stop sign. The entire
police investigative division has gone on
vacation to Bora Bora to relax, so the mayor
has contracted with you and your team of
experts to determine what happened and
what traffic laws were broken.
In order to solve this portion of the lab we have to use a kinematics equation from an earlier chapter.
Vf^(2 )=Vi^2+2a∆x
We then plug in what we know from the information given to us in the problem. We know that the SUV has
a mass of 3000kg, and the Wagon has a mass of 2000kg. We also know that the acceleration of the SUV
with its brakes locked is -2m/s^2, and that the acceleration of the Wagon with its brakes locked is -3m/s^2.
We then use this information to solve two kinematics problems, one for the final velocity of the wagon, the
other for the final velocity of the SUV.
Vf^2=(0)^2+2(-3m/s^2 )(24)
Vf^2= -144
Vf^2= √144
Vf=12 m/s
Vf^2=(0)^2+2((-2m)/s^2 )(2)
Vf^2= -8
Vf^2= √8
Vf=2.8 m/s
So immediately after the collision the Subaru wagon had a velocity of 12 m/s. The SUV had a velocity of 2.8
I had to find the initial velocity of the SUV
using the equation I found the SUV was
traveling at a speed of 10.8 meters per
second when it rear ended the Wagon
X= Wagon Y= SUV
(_ )()+(_ )()=(_ )()+(_ )(
(0)(2000)+(_ )(3000)=(12)(2000)+(2.8)(3000)
0+(_ )(3000)=24000+8400
(_ )(3000)=32400
(_ )=10.8 /
In the world of physics there are three types of collisions, these types are
known as elastic, inelastic and perfectly inelastic. An Elastic Collision is
when two objects collide and bounce off of each other with no
deformation and have the same kinetic energy before and after the
collision. An Inelastic Collision is exactly the opposite, with two objects
colliding and a deformation occurring. A Perfect Inelastic collision
occurs when two objects collide and move together as one object
(such as throwing two pieces of clay together.
This crash exhibits characteristics of an inelastic collision. This is due
to the fact that the two vehicles did dot stay joined together after the
collision (the two vehicles had different final velocities). Using the kinetic
energy formula (KE= ½ m*v^2) you can determine that the kinetic
energies for the vehicles is different in the beginning than it is in the end.
Before: KEsuv= ½ (3000)x (10.8^2)= 174.96 KJ
KEwag= ½ (2000)x (0^2)= 0 KJ
After: KEsuv= ½ (3000)x (2.8^2)= 11.76 KJ
KEwag= ½ (2000)x (12^2)= 144 KJ
If added together the kinetic energies do not match (note: some energy
is given off as heat) (174.96 does not = 155.76). So the only collision type
left is an inelastic collision
The cars collided with the SUV having a
velocity of 10.8 m/s. The Subaru was at
rest. After the accident the cars had a
velocity of 12 m/s (Subaru) and 2.8 m/s
(SUV). The type of collision that the cars
experienced was a inelastic collision.

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