Physics midterm question: net force on pushed-down book

Physics 205A Midterm 1, fall semester 2013
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 4.37

A force of 1.0 N pushes down on a 0.50 kg book, which is stationary on a table. The direction of the net force on the book is:
(A) downwards.
(B) (has no direction, as the net force is zero.)
(C) upwards.
(D) (Not enough information given.)

Correct answer (highlight to unhide): (B)

Since the book is stationary, its motion is constant (with zero velocity). Thus the net force of all the forces acting on the book must equal zero, due to Newton's first law.

Sections 70854, 70855, 73320
Exam code: midterm01p0To
(A) : 12 students
(B) : 57 students
(C) : 4 students
(D) : 0 students

Success level: 78%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.24