Two simple pendulums having lengths $l_1$ and $l_2$ with negligible string mass undergo angular…

Two simple pendulums having lengths $l_1$ and $l_2$ with negligible string mass undergo angular displacements $\theta_1$ and $\theta_2$, from their mean positions, respectively. If the angular accelerations of both pendulums are same, then which expression is correct?
  1. $\theta_1 l_2^2=\theta_2 l_1^2$
  2. $\theta_1 l_1=\theta_2 l_2$
  3. $\theta_1 l_1^2=\theta_2 l_2^2$
  4. $\theta_1 l_2=\theta_2 l_1$

Solution

$\begin{aligned} & \omega=\sqrt{\frac{\mathrm{g}}{\ell}} \\ & \alpha=-\omega^2 \theta \\ & \therefore \frac{\mathrm{~g}}{\ell_1} \theta_1=\frac{\mathrm{g}}{\ell_2} \theta_2 \\ & \Rightarrow \theta_1 \ell_2=\theta_2 \ell_1\end{aligned}$

Asked in: JEE Main 2025 (04 Apr Shift 1)

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