Physics Fluid Dynamics PMDC Conceptual Practice
PMDC Verified Question 31 of 37
Which of the following algebraic expressions correctly represents the mass flow rate (mass flowing per second) of a fluid in a pipe?
A
\( \rho A v \)
B
\( A v \)
C
\( \rho v \)
D
\( A v / \rho \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option A: \( \rho A v \)
Concept:

Mass flow rate dictates how many kilograms of a fluid pass through a cross-section per unit time.

Formula:

$$ \dot{m} = \frac{m}{t} = \rho \frac{V}{t} $$

Solution:

  • Density is mass per unit volume: \( m = \rho \times \text{Volume} \).
  • The volume of a cylindrical fluid segment is Area \( \times \) distance (\( V = A \cdot d \)).
  • Mass per time \( = \frac{\rho \cdot A \cdot d}{t} \).
  • Since distance over time (\( d/t \)) is velocity (\( v \)), the formula simplifies directly to \( \rho A v \).


Why other options are incorrect:

Option B (\( A v \)) is the volume flow rate. Option C (\( \rho v \)) is mass flux per unit area. Option D divides by density, which makes no physical sense.

Quality & Fidelity Assurance: Every question on BeambePrep is rigorously curated against the official PMDC syllabus with zero filler, zero out-of-syllabus content, and zero typos. When an authentic past paper originally contained a historical mistake or ambiguity from the examining board (such as UHS or NUMS), BeambePrep faithfully reflects the original paper while detailing the nuance and scientific consensus in the autopsy above.

Previous Question All Fluid Dynamics MCQs Next Question

Want to solve full-length papers under timed exam conditions?

Practice with zero-scroll lockdown sprints, dynamic latency zone timers, live peer selection telemetry, and the automated Amber mistake recovery loop.

Enter Arena Sprint iOS App Android App