Physics Force & Motion DUHS 2022
PMDC Verified Question 81 of 137
A bullet is fired horizontally with 20m/s. In the absence of air friction, its horizontal velocity after 2 seconds will be:
A
\( 10 \text{ ms}^{-1} \)
B
\( 5 \text{ ms}^{-1} \)
C
\( 20 \text{ ms}^{-1} \)
D
\( 40 \text{ ms}^{-1} \)
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option C: \( 20 \text{ ms}^{-1} \)
Concept:

Newton's First Law of motion states an object will maintain constant velocity unless acted on by an external force.

Solution:

  • A projectile in flight experiences only one force: gravity, which acts strictly vertically downwards.


  • Because there is zero air friction, there are absolutely no horizontal forces acting on the bullet.


  • Therefore, horizontal acceleration is zero, and the horizontal velocity remains exactly \( 20 \text{ m/s} \) for the entire duration of the flight (Option C).


Why other options are incorrect:

Options A and B incorrectly assume deceleration. Option D wrongly multiplies velocity by time or assumes horizontal acceleration exists.

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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