If length of oscillating simple pendulum is made $\frac{1}{3}$ times at a place keeping amplitude same, then…

If length of oscillating simple pendulum is made $\frac{1}{3}$ times at a place keeping amplitude same, then its total energy (E) will be
  1. $6 \mathrm{E}$
  2. $4 \mathrm{E}$
  3. $2 \mathrm{E}$
  4. $3 \mathrm{E}$

Solution

$T=2 \pi \sqrt{\frac{\ell}{g}}$ $\frac{2 \pi}{\omega}=2 \pi \sqrt{\frac{\ell}{g}}$ $\omega=\sqrt{\frac{\mathrm{g}}{\ell}} \quad \therefore \omega \propto \frac{1}{\sqrt{\ell}}$ $\therefore \frac{\omega_{2}}{\omega_{1}}=\sqrt{\frac{\ell_{1}}{\ell_{2}}}=\sqrt{\frac{\ell_{1}}{\ell_{1} / 3}}=\sqrt{3}$ $\therefore \omega_{2}=\sqrt{3} \omega_{1}$ Now $E \propto \omega^{2}$ $\therefore \frac{\mathrm{E}_{2}}{\mathrm{E}_{1}}=\frac{\omega_{2}^{2}}{\omega_{1}^{2}}=3$ $\therefore E_{2}=3 E_{1}$

Asked in: MHT CET 2020 (20 Oct Shift 1)

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