## 20121123

### Physics quiz question: acceleration of SHM object

Physics 205A Quiz 6, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Multiple-Choice Question 10.7

A 1.2 kg mass attached to a horizontal spring has a 8.0 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 net force on the mass is zero?
(A) 0 s.
(B) 2 s.
(C) 4 s.
(D) 6 s.

The net force on an object is related to its acceleration (and mass):

ΣF = m·a,

where the acceleration a is the derivative of the velocity, or the slope of the velocity graph:

a = dv/dt = slope of v.

So for the net force to be zero, the acceleration must be zero, and this occurs when the velocity graph has zero slope, which occurs at t = 2 s and 6 s.

Sections 70854, 70855
Exam code: quiz06How3
(A) : 13 student
(B) : 25 students
(C) : 8 students
(D) : 0 students

Success level: 54%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.50