$\omega=\sqrt{\frac{g}{\alpha}}$
$\frac{2 \pi}{\mathrm{T}}=\sqrt{\frac{\mathrm{g}}{\alpha}} \quad \text { or } \quad \mathrm{T}=2 \pi \sqrt{\frac{\alpha}{\mathrm{g}}}$
$Y = A \sin (\pi t +\phi)$, where time is measured in $second$.
The length of pendulum is .............$cm$
Simultaneously at $t=0$, a small pebble is projected with speed $v$ from point $P$ at an angle of $45^{\circ}$ as shown in the figure. Point $P$ is at a horizontal distance of $10 \ cm$ from $O$. If the pebble hits the block at $t=1 \ s$, the value of $v$ is (take $g =10 \ m / s ^2$ )