Physics Force & Motion NUMS 2024
PMDC Verified Question 14 of 137
A ball with momentum 8 kg m/s hits a wall and bounces straight back without losing K.E. the change in momentum of this ball is:
A
4 Ns
B
-16 Ns
C
16 Ns
D
8 Ns
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: -16 Ns
Concept:

Momentum is a highly directional vector. Bouncing reverses the direction entirely.

Formula:

$$ \Delta P = P_f - P_i $$

Solution:

  • Because it doesn't lose K.E., the collision is perfectly elastic, meaning it bounces back with the exact same speed.


  • Initial momentum \( P_i = +8 \text{ kg m/s} \).


  • Final momentum (reversed direction) \( P_f = -8 \text{ kg m/s} \).


  • Change in momentum: \( \Delta P = -8 - 8 = -16 \text{ Ns} \) (or kg m/s).


Why other options are incorrect:

If one ignores direction, \( 8 - 8 = 0 \). Adding them incorrectly ignores the definition of a "change" (final - initial).

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 Force & Motion 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