Physics Force & Motion ETEA 2023
PMDC Verified Question 41 of 137
Neglecting the effect of air resistance how long a stone takes to dropped of a 125 m high building lands on the ground, take g = \( 10 \text{ m/s}^2 \):
A
3 sec
B
4 sec
C
18 sec
D
5 sec
Tap any option to test your recall and reveal the step-by-step Propolis autopsy.

Propolis Cognitive Error Autopsy

Official Correct Choice:
Option D: 5 sec
Concept:

The time taken for an object dropped from rest to hit the ground strictly depends on the height and gravity.

Formula:

$$ S = v_it + \frac{1}{2}gt^2 $$

Solution:

  • Because it is dropped, initial velocity \( v_i = 0 \).


  • Height \( S = 125 \text{ m} \).


  • Gravity \( g = 10 \text{ m/s}^2 \).


  • Substitute: $$ 125 = (0)t + \frac{1}{2}(10)t^2 $$


  • $$ 125 = 5t^2 \implies t^2 = \frac{125}{5} = 25 $$


  • Take the square root: \( t = 5 \text{ seconds} \).


Why other options are incorrect:

Failing to take the square root results in 25. Ignoring the \( 1/2 \) multiplier gives roughly 3.5s. Simple arithmetic errors lead to the other values.

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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