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Question

Savitha, a XI standard student, while conducting an experiment to determine the effective length of a simple pendulum L, notes down the data of time taken to complete 30 oscillations as $60 \text{ s}$ and hence calculates the length of the simple pendulum as :
(Take $\pi^2 = 9.8$, and $g = 9.8 \text{ m/s}^2$)

This question was previously asked in
NEET UG Re-Exam 2026 Question Paper (21-Jun-2026)
The correct answer is
$1 \text{ m}$

Calculating Simple Pendulum Length

To determine the effective length of the simple pendulum, follow these steps:

  1. Calculate the Time Period (T): The time period is the time taken for one complete oscillation. Given the time for 30 oscillations is 60 s, calculate T.

    $ T = \frac{\text{Total time}}{\text{Number of oscillations}} = \frac{60 \text{ s}}{30} = 2 \text{ s} $

  2. Use the Simple Pendulum Formula: The formula for the time period of a simple pendulum is:

    $ T = 2\pi\sqrt{\frac{L}{g}} $

    Where \( L \) is the length of the pendulum and \( g \) is the acceleration due to gravity.
  3. Rearrange Formula for Length (L): To find the length \( L \), rearrange the formula:

    Square both sides: \( T^2 = 4\pi^2 \frac{L}{g} \)

    Isolate \( L \): \( L = \frac{gT^2}{4\pi^2} \)

  4. Substitute Values and Compute Length: Use the given values: \( g = 9.8 \text{ m/s}^2 \), \( T = 2 \text{ s} \), and \( \pi^2 = 9.8 \).

    $ L = \frac{(9.8 \text{ m/s}^2) \times (2 \text{ s})^2}{4 \times 9.8} $

    $ L = \frac{9.8 \times 4 \text{ m}}{4 \times 9.8} $

    $ L = 1 \text{ m} $

Therefore, the calculated length of the simple pendulum is 1 m.

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