Physics flashcard question: acceleration at highest point in trajectory

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

Students were asked in the middle of their learning cycle the following think-pair-share question, to be answered using flashcards.

The velocity vector components of a projectile trajectory is shown. Air resistance is negligible.

At the highest point in the trajectory, which acceleration component is zero?
(A) a_x.
(B) a_y.
(C) (Both of the above choices.)
(D) (None of the above choices.)
(E) (Unsure/guessing/lost/help!)

Sections 70854, 70855 (pre-)
(A) : 15 students
(B) : 17 students
(C) : 3 students
(D) : 3 students
(E) : 4 students

This question was asked again after students were instructed to discuss with a neighbor how they chose their answer, and to convince each other why their answer is (in)correct.

Sections 70854, 70855 (post-)
(A) : 20 students
(B) : 7 students
(C) : 5 students
(D) : 1 student
(E) : 5 students

Correct answer: (A)

Pre- to post- peer-interaction gains:
pre-interaction correct = 36%
post-interaction correct = 53%
Hake (normalized) gain <g> = 27%

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