Physics quiz question: descending, widening pipe

Physics 205A Quiz 5, fall semester 2012
Cuesta College, San Luis Obispo, CA

Cf. Giambattista/Richardson/Richardson, Physics, 2/e, Problem 9.41

Water flows through a pipe from point [1] to point [2]. Assume ideal fluid flow. The speed of the water __________ as it flows from point [1] to point [2].
(A) decreases.
(B) remains constant.
(C) increases.
(D) (Not enough information is given.)

Correct answer: (A)

From applying the continuity equation:

A₁·v₁ = A₂·v₂,

the water speed at point [2] is slower than at point [1], because the cross-sectional area at point [2] is larger than at point [1].

Sections 70854, 70855
Exam code: quiz05L4mN
(A) : 34 students
(B) : 9 students
(C) : 8 students
(D) : 1 student

Success level: 65%
Discrimination index (Aubrecht & Aubrecht, 1983): 0.55