Physics quiz question: banana slug speed

Physics 205A Quiz 1, Fall Semester 2009
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 1.25

The speed of a large banana slug (http://hypertextbook.com/facts/AngieYee.shtml) has been timed at 0.0023 cm/s. What is this speed in miles per hour? There are 1,609 m in one mile.
(A) 4.0e-8 mi/hr.
(B) 5.1e-5 mi/hr.
(C) 8.6e-5 mi/hr.
(D) 1.0e-3 mi/hr.

Correct answer: (B)

To convert cm/s into mi/hr:

(0.0023 cm/s) * (1 m/100 cm) * (1 mi/1,609 m) * (3,600 s/1 hr) = 5.1e-5 mi/hr.

Response (A) is 0.0023*100/(3,600*1,609); response (C) is 0.0023*60/1,609; response (D) is 0.0023*1,609/3600.

Student responses
Sections 70854, 70855
(A) : 3 students
(B) : 43 students
(C) : 9 students
(D) : 0 students

Success level: 78%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.91