Physics quiz question: direction of motion on vx(t) graph

Physics 205A Quiz 2, fall semester 2014
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 2.11

A v_x(t) graph of an object traveling along a straight line is shown at right. The object starts at x = 0 at t = 0. The object is traveling in the +x direction at:
(A) t = 1 s.
(B) t = 3 s.
(C) t = 5 s.
(D) (More than one of the above choices.)

Correct answer (highlight to unhide): (C)

From 0 s < t < 4.5 s, the object has negative v_x values, and thus is moving in the –x direction at t = 1 s and t = 3 s. From 4.5 s < t < 6 s, the object has positive v_x values, and thus is moving in the +x direction at t = 5 s.

Sections 70854, 70855, 73320
Exam code: quiz02T1o9
(A) : 3 students
(B) : 1 students
(C) : 35 students
(D) : 31 students

Success level: 50%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.82