20121130

Physics midterm question: SHM object at equilibrium

Physics 205A Midterm 2, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Multiple-Choice Questions 10.11-10.20

A 0.60 kg mass attached to a horizontal spring has a 4.0 s period of oscillation. Neglect friction and drag. The velocity versus time graph for this mass-spring system is shown at right. What is the earliest time that the mass is at the equilibrium point?
(A) 0 s.
(B) 1 s.
(C) 2 s.
(D) 3 s.

Correct answer: (A)

When the mass is at the equilibrium point (x = 0), it will have zero elastic potential energy (Uelas = (1/2)·k·x2), which means it must have its maximum amount of translational kinetic energy (Ktr = (1/2)·m·v2). This occurs when the mass has its maximum speed, which occurs at t = 0 s, 2 s, and 4 s.

Sections 70854, 70855
Exam code: midterm02gL0u
(A) : 18 students
(B) : 17 students
(C) : 19 students
(D) : 0 students

Success level: 33%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.34

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