Physics - W.E.P. Question with Solution | TestHub

Let the mass of the pendulum be $m$ and its length be $L$.

When the pendulum is released from a $90^{\circ }$ angle, it falls through a vertical height $L$ to reach the mean position.

By conservation of mechanical energy, the potential energy lost is converted into kinetic energy at the lowest point:

$mgL=\frac{1}{2}m{v}^2$

$v^2=2gL$

At the mean position, the tension $T$ in the string and the weight $mg$ provide the necessary centripetal force:

$T-mg=\frac{m{v}^2}{L}$

Substituting the value of $v^2$:

$T=mg+\frac{m(2gL)}{L}$

$T=mg+2mg=3mg$

The maximum tension occurs at the mean position, so the string must be able to withstand a tension of $3mg$.

Answer: 3 mg