Physics quiz question: fastest speed on vx(t) graph

Physics 205A Quiz 2, fall semester 2013
Cuesta College, San Luis Obispo, CA

The 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 experiences its greatest speed at:
(A) 2 s < t < 3 s.
(B) t = 3 s.
(C) 3 s < t < 6 s.
(D) (More than one of the above choices.)

Correct answer (highlight to unhide): (B)

The object is moving in the +x direction, where it speeds up from 0 m/s to +1 m/s from 2 s < t < 3 s; and slows down from +1 m/s to 0 m/s from 3 s < t < 6 s. Thus the object has its greatest speed at t = 3 s. (The slope of this v_x(t) graph is the acceleration a_x of the object, which is + 1 m/s² from 2 s < t < 3 s; and a_x = –0.3 m/s² from 3 s < t < 6 s.)

Sections 70854, 70855, 73320
Exam code: quiz02p3nG
(A) : 34 students
(B) : 32 students
(C) : 3 students
(D) : 0 students

Success level: 46%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.68