Physics 204A
THIRD EXAM Chapters 1  11
Fall 2006
1
Name:_________________________________________
Solve the following problems in the space provided. Use the back of the page if needed. Each problem is
worth 20 points. You must
show your work in a logical fashion starting with the correctly applied
physical principles. The equations you need are on the equation sheet. Your score will be maximized if
your work is easy to follow because partial credit will be awarded.
1. I saw the sketch below in the newspaper last summer. The author explained the benefits of using
cable barriers instead of concrete on highways in simple terms. Now, you need to explain the same thing
using the principles of physics.
The physics principle involved is the ImpulseMomentum Theorem.
"
p
=
Fdt
#
The change in momentum of a car colliding with the barrier is the same whether the barrier is made of
concrete or cables because whatever the original momentum, it will presumably be reduced to zero. The
difference between the barriers is on the right side of the equation. If the barrier is made of concrete, the
time to bring the car to rest is very short compared to the time for a cable barrier. Therefore, the force
exerted by the concrete barrier must be much larger than the force exerted by the cables. If the force on
the car is smaller, damage to the vehicle and its passengers will be reduced.
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 Fall '09
 Kagan
 Angular Momentum, Force, Work, angular momentum vector, Exam Chapters

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