Physics quiz question: speed and direction

Physics 205A Quiz 2, fall semester 2011
Cuesta College, San Luis Obispo, CA

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

Consider this v_x(t) graph of an object traveling in a straight line. The object starts at x = 0 at t = 0. From t = 6 s to t = 10 s, the object __________ while moving in the __________ direction.
(A) slows down, positive.
(B) speeds up, positive.
(C) slows down, negative.
(D) speeds up, negative.

Correct answer: (D)

From t = 6 s to t = 10 s, speed increases in the negative direction, (with constant acceleration) with velocity changing from v_x = 0 to v_x = -4 m/s.

Sections 70854, 70855
Exam code: quiz02p4iN
(A) : 5 students
(B) : 1 student
(C) : 10 students
(D) : 37 students

Success level: 70%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.33