Two block of masses 1 kg and 2 kg are connected by a metal wire going over a smooth in figure. The breaking stress of the metal is $2 \times 10^{9} \;N/m^2$. What should be the minimum radius of the wire used if it is not to break? Take $g=10\;ms^2$

Question

$$\begin {array} {1 1} (a)\;4.6 \times 10^{-5}\;m & \quad (b)\;4.6 \times 10^{-6}\; m \\ (c)\;2.5 \times 10^{-6}\;m & \quad (d)\;2.5 \times 10^{-5}\;m \end {array}$$