Physics Work & Energy ETEA 2018
PMDC Verified Question 86 of 108
If the momentum of a body decreases by 20% the percentage decreases in K.E will be:
A
44%
B
36%
C
28%
D
20%
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option B: 36%
Concept:

Kinetic energy is directly proportional to the square of momentum.

Formula:

$$ K.E = \frac{p^2}{2m} \implies K.E \propto p^2 $$

Solution:

  • Let initial momentum be \( p_1 = 100 \). Initial K.E \( \propto (100)^2 = 10000 \).


  • A 20% decrease means new momentum \( p_2 = 80 \).


  • New K.E \( \propto (80)^2 = 6400 \).


  • Decrease in K.E = 10000 - 6400 = 3600.


  • Percentage decrease = \( \frac{3600}{10000} \times 100\% = 36\% \).


Why other options are incorrect:

Directly assuming K.E decreases by the same 20% ignores the squared relationship. 44% is the answer for a 20% increase in momentum.

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 Work & Energy 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