Physics quiz question: mass-spring translational kinetic energy

Physics 205A Quiz 6, fall semester 2015
Cuesta College, San Luis Obispo, CA

A 0.40 kg mass attached to a horizontal spring oscillates with an amplitude of 0.20 m. Ignore friction/drag. This mass-spring system has zero translational kinetic energy at:
(A) x = 0.
(B) x = +0.20 m.
(C) (Both of the above choices.)
(D) (None of the above choices.)

Correct answer (highlight to unhide): (B)

Since there is no work done on or by this mass-spring system, its total mechanical energy is a constant:

E = KE_tr + PE_elas,

E = (1/2)·m·v² + (1/2)·k·x².

If there is zero translational kinetic energy, then KE_tr = 0, and the total mechanical energy is solely comprised of elastic potential energy, which would be a maximum at x = +0.20 m (as well as at x = –0.20 m).

(If there is zero elastic potential energy, then PE_elas = 0, and the total mechanical energy is solely comprised of translational kinetic energy, which would be a maximum at x = 0.)

Sections 70854, 70855, 73320
Exam code: quiz06m45S
(A) : 10 students
(B) : 63 students
(C) : 0 students
(D) : 0 students

Success level: 85%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.26