Physics Fluid Dynamics PMDC Conceptual Practice
PMDC Verified Question 22 of 37
Which of the following describes the correct graphical relationship between the drag force \( F \) acting on a small spherical object and its low velocity \( v \) moving through a viscous fluid?
A
An exponentially decaying curve.
B
A straight line passing through the origin.
C
A parabola opening upwards.
D
A horizontal straight line parallel to the x-axis.
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: A straight line passing through the origin.
Concept:

At low speeds, the drag force on a spherical object is determined strictly by Stokes' Law, which represents a direct, linear proportionality.

Formula:

$$ F = (6 \pi \eta r) \cdot v \implies y = m x $$

Solution:

  • The equation represents a linear function where \( F \) is the y-variable, \( v \) is the x-variable, and the constant \( (6 \pi \eta r) \) is the slope \( m \).
  • Since there is no y-intercept term, the line starts at \( (0,0) \).
  • Therefore, plotting \( F \) vs \( v \) yields a straight line passing through the origin.



vF

Why other options are incorrect:

A parabola would occur at high velocities where drag is proportional to \( v^2 \). A horizontal line implies drag is independent of speed, which is false.

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.

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