Q109 / 150 · MHT CET 2025 (26 Apr Shift 1) · Physics

At a place, the length of the oscillating simple pendulum is made $\frac{1}{4}$ times keeping amplitude same then the total energy will be

  • A
    2 times
  • Correct answer
    B
    4 times
  • C
    8 times
  • D
    16 times

Solution

The total energy for a simple pendulum in harmonic motion is $E = \frac{1}{2} m \omega^2 A^2$ with angular frequency $\omega = \sqrt{\frac{g}{L}}$. Substituting gives $E = \frac{1}{2} m \frac{g}{L} A^2$.

For initial length $L_1$, the energy is $E_1 = \frac{1}{2} m \frac{g}{L_1} A^2$. When the length becomes $L_2 = \frac{1}{4} L_1$ with amplitude unchanged, the new energy becomes

$E_2 = \frac{1}{2} m \frac{g}{\frac{1}{4} L_1} A^2 = 4 \left(\frac{1}{2} m \frac{g}{L_1} A^2\right) = 4 E_1$

The total energy increases by a factor of 4.

Final answer: $\boxed{\text{B}}$

Hence, the correct answer is option: 'B'.

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