20161028

Physics quiz question: classification of staged car collision

Physics 205A Quiz 4, fall semester 2016
Cuesta College, San Luis Obispo, CA

"Accident Reconstruction Example"
Evans Accident Reconstruction
evansar.com/example.html

A crash was staged[*] between a 1997 Pontiac Grand Am[**] (mass 1.30×103 kg) traveling at 17 m/s and a stationary 1991 Volkswagen Jetta[**] (mass 1.47×103 kg). Both cars sustained significant damage, and completely separated from each other after the collision. Ignore friction, drag, and external forces during this brief collision. This collision is:
(A) completely inelastic.
(B) (partially) inelastic.
(C) elastic.
(D) (None of the above choices.)

[*] evansar.com/example.html.
[**] thecarconnection.com/specifications/pontiac_grand-am_1997_4dr-sdn-se.
[***] automobile-catalog.com/make/volkswagen/jetta_2gen/jetta_2gen/1991.html.

Correct answer: (B)

Negligible net external force and brief time duration for this collision makes the external impulse on this system zero, such that momentum is conserved. Since both cars sustained significant damage, translational kinetic energy is not conserved, and so this collision cannot be elastic. As both cars separated from each other after the collision, this collision cannot be a completely inelastic collision, and this collision must then be classified as (partially) inelastic.

Sections 70854, 70855, 73320
Exam code: quiz04th1R
(A) : 2 students
(B) : 44 students
(C) : 4 students
(D) : 1 student

Success level: 86%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.36

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