In a certain observation of experiment with simple pendulum we get $l=23.2 \mathrm{cm}$, $r=1.32 \mathrm{cm}$ and time taken for 20 oscillations was $20.0 sec$. Taking ${\pi }^2=10$, find the value of g in proper significant figures.

Equivalent length of pendulum,

$L=23.2 \mathrm{cm}+1.32 \mathrm{cm}=24.52 \mathrm{cm}$

$=24.5 \mathrm{cm}$ (according to addition rule of significant figures)

Time period, $T=\frac{20.0}{20}=1.00 \mathrm{s}$. Time period has 3 significant figures

$g=\left(4{\pi }^2\right)\frac{l}{T^2}=\frac{4\times 10\times 24.5\times {10}^{-2}}{(1.00{)}^2}=9.80 \mathrm{m}/{\mathrm{s}}^2$