Physics clicker question: no-drag projectile motion

Physics 205A, Fall Semester 2008
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Figure 3.17

Students were asked the following clicker question (Classroom Performance System, einstruction.com) at the start of their learning cycle.

In general, which of the following quantities is zero, for a projectile with negligible air resistance?
(A) v_x.
(B) v_y.
(C) a_x.
(D) a_y.
(E) (More than one of the above choices.)
(F) (None of the above choices.)
(G) (I'm lost, and don't know how to answer this.)

Sections 70854, 70855
(A) : 6 students
(B) : 3 students
(C) : 14 students
(D) : 3 students
(E) : 7 students
(F) : 3 students
(G) : 8 students

This question was asked again after displaying the tallied results with the lack of consensus, with the following results. No comments were made by the instructor, in order to see if students were going to be able to discuss and determine the correct answer among themselves.

Sections 70854, 70855
(A) : 4 students
(B) : 2 students
(C) : 27 students
(D) : 0 students
(E) : 5 students
(F) : 4 students
(G) : 3 students

Correct answer: (C)

Under these ideal conditions, the horizontal component of velocity will be constant, and thus the horizontal component of acceleration will be zero. Realistically, with air resistance, (F) would be the most correct response.

Pre- to post- peer-interaction gains:
pre-interaction correct = 32%
post-interaction correct = 60%
Hake, or normalized gain <g> = 41%