Physics quiz question: volume flow rate

Physics 205A Quiz 5, Fall Semester 2009
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 9.45

[Version 1]
Water flows through a pipe with a speed of 1.5 m/s through a pipe of 0.10 m inside radius, at point [1]. The pipe has the same inside radius of 0.10 m at point [2], at a height higher than point [1]. Assume ideal fluid flow. What is the volume flow rate of water at point [1]?
(A) 0.047 m^3/s.
(B) 0.94 m^3/s.
(C) 15 m^3/s.
(D) 23 m^3/s.

Correct answer: (A)

The volume flow rate is given by A*v, where the area A = pi*r^2, and v is the speed.

Response (B) is 2*pi*r*v (circumference times speed?); response (C) is v/r (angular speed?); and response (D) is v^2/r (radial acceleration?).

Student responses
Sections 70854, 70855
(A) : 30 students
(B) : 8 students
(C) : 10 students
(D) : 0 students

Success level: 62%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.44

[Version 2]
Water flows through a pipe with a speed of 1.5 m/s through a pipe of 0.10 m inside radius, at point [1]. The pipe has the same inside radius of 0.10 m at point [2], at a height lower than point [1]. Assume ideal fluid flow.
(A) 0.047 m^3/s.
(B) 0.94 m^3/s.
(C) 15 m^3/s.
(D) 23 m^3/s.

Correct answer: (A)

Student responses
Section 72177
(A) : 11 students
(B) : 0 students
(C) : 1 student
(D) : 0 students

Success level: 91%
Discrimination index (Aubrecht & Aubrecht, 1983): 0