In a vertical circular motion, the tension ($T$) in the wire varies depending on the position of the mass $m$. According to Newton’s Second Law, the net centripetal force at any point making an angle $\theta$ with the downward vertical is $T - mg \cos \theta = \frac{mv^2}{R}$, where $R$ is the radius . This gives the tension as $T = \frac{mv^2}{R} + mg \cos \theta$ . At the lowest point, $\theta = 0^{\circ}$ (so $\cos \theta = 1$) and the velocity $v$ is at its maximum because gravitational potential energy is converted into kinetic energy as the mass descends . Consequently, the tension $T$ reaches its maximum value at this point, making the wire most likely to break .