Physics quiz question: rope, pulley, suspended box

Physics 205A Quiz 3, fall semester 2011
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problems 4.74, 4.75

A 1.0 kg box is suspended by use of an ideal pulley and rope. Neglect the weights of the pulley and rope. The magnitude of the net force on the 1.0 kg box is:
(A) 0 N.
(B) some value between 0 and 9.8 N.
(C) 9.8 N.
(D) some value greater than 9.8 N.
(E) (Not enough information is given.)

Correct answer (highlight to unhide): (A)

Since the box is stationary, then the forces acting on it must sum to zero, according to Newton's first law.

Sections 70854, 70855
Exam code: quiz03Fn37
(A) : 26 students
(B) : 6 students
(C) : 18 students
(D) : 3 students
(E) : 2 students

Success level: 47%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.78