Cuesta College, San Luis Obispo, CA
A Physics 205A student asked the following question on an online reading assignment[*]:
Can pressure increase as the radius of a pipe with flowing water increases?Discuss a plausible horizontal pipe system that would result in this happening. Explain your reasoning using the continuity equation, Bernoulli's equation, and the properties of ideal fluid flow.
Solution and grading rubric:
Correct. Discusses/demonstrates the application of ideal fluid conservation laws for a horizontal pipe with a narrow cross-section at point  and a wider cross-section at point :
- continuity, where the widening of the pipe at point  will cause a corresponding slower speed there;
- energy density (Bernoulli's equation), as the speed decreases (making the (1/2)⋅ρ⋅Δ(v2) term negative) and the elevation is not changing (making the ρ⋅g⋅Δy term zero) for the fluid flowing from point  to point , then in order for all three terms on the right-hand side of Bernoulli's equation to sum to zero, the ΔP term would need to be positive, and thus pressure would increase flowing from point  to point .
Nearly correct, but includes minor math errors.
Nearly correct, but approach has conceptual errors, and/or major/compounded math errors.
Implementation of right ideas, but in an inconsistent, incomplete, or unorganized manner. Some garbled attempt at applying continuity and Bernoulli's equation.
Implementation of ideas, but credit given for effort rather than merit. Approach other than that of applying continuity and Bernoulli's equation.
Irrelevant discussion/effectively blank.
Sections 70854, 70855, 73320
Exam code: midterm02oPt0
p: 36 students
r: 4 students
t: 9 students
v: 3 students
x: 4 students
y: 0 students
z: 0 students
A sample "p" response (from student):