To break a wire of one meter length, minimum 40 kg-wt is required. Then the wire of the same material of double radius and 6 m length will require breaking weight

$\therefore$Breaking force = Breaking stress x Area of cross section of wire

 Breaking force $\propto {\mathrm{r}}^2$ (Breaking distance is constant) If radius becomes doubled, then breaking force will become 4 times i.e. 40 x 4 = 160 kg wt