Physics clicker question: pressed-down book

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

Cf. Giambattista/Richardson/Richardson, Physics, 1/e, Problem 4.51

Students were asked the following clicker questions (Classroom Performance System, einstruction.com) near the beginning of their learning cycle:

Mass of book = 0.50 kg.
Coefficient of static friction mu_s = 0.45.
Coefficient of kinetic friction mu_k = 0.40.

You push down on the book with a force of 1.0 N. The normal force of the table on the book has a magnitude of:
(A) 4.9 N.
(B) 1.0 N.
(C) 4.9 N – 1.0 N.
(D) 4.9 N + 1.0 N.
(E) (I'm lost, and don't know how to answer this.)

Sections 70854, 70855
(A) : 3 students
(B) : 13 students
(C) : 2 students
(D) : 16 students
(E) : 4 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) : 0 students
(B) : 5 students
(C) : 0 students
(D) : 32 students
(E) : 1 student

Correct answer: (D)

The book has the weight force of the Earth pulling down on it (4.9 N), the applied force (1.0 N) pushing down on it, and since Newton's first law applies, the normal force of the table pushing up on the book is 5.9 N in magnitude.

Pre- to post- peer-interaction gains:
pre-interaction correct = 42%
post-interaction correct = 84%
Hake, or normalized gain <g> = 72%

This question was asked in a previous semester (Fall 2007), but with students who were not adequately coached on the think-(pair)-share methodology.