A simple pendulum consists of a $50 \mathrm{~cm}$ long string connected to a $100 \mathrm{~g}$ ball. The ball is pulled aside so that the string makes an angle of $37^{\circ}$ with the vertical and is then released. Find the tension in the string when the bob is at its lowest position.
$\cos \theta=\frac{A C}{A B}$
and
$\mathrm{AC}=\mathrm{AB} \cos \theta$
$A C=0.4$
and
$C D=A D-A C$
$C D=0.1 \mathrm{~m}$
Energy is same at $B$ and $D$
$\frac{1}{2} m v^{2}=m g h$
$\frac{\frac{1}{2}}{2} \mathrm{v}^{2}=10 \times 0.1$
$\mathrm{v}=\sqrt{2}_{\mathrm{m} / \mathrm{s}}$
Tension $\mathrm{T}=\left(\mathrm{mv}^{2}\right) / \mathrm{r}+\mathrm{mg}$
$\mathrm{T}=(0.1 \times 2) / 0.5+0.1 \times 10$
$\mathrm{T}=1.4 \mathrm{~N}$
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