Question
A simple pendulum makes 60 oscillations per minute. Find its effective length.

Answer

60 time of oscillation= $1 min=60 sec$
$\therefore 1$ oscillation time $=\frac{60}{60}=1 sec$
$\begin{array}{l}\text {We know}\quad l=\frac{g T^2}{4 \pi^2}=\frac{9.8 \times(1)^2}{4 \times 9.86}\left(\because \pi^2=9.86\right) \\\quad \quad \quad \quad\quad l=\frac{9.8}{39.44}=0.2485 m\end{array}$
Hence, effective length $=0.2485 m$

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