Two blocks of masses m and M are connected by means of a metal wire of cross-sectional area A passing over a frictionless fixed pulley as shown in the figure. The system is then released. If $\mathrm { M } = 2 \mathrm {~m}$, then the stress produced in the wire is:\\
(1) $\frac { 2 \mathrm { mg } } { 3 \mathrm {~A} }$\\
(2) $\frac { 4 \mathrm { mg } } { 3 \mathrm {~A} }$\\
(3) $\frac { \mathrm { mg } } { \mathrm { A } }$\\
(4) $\frac { 3 \mathrm { mg } } { 4 \mathrm {~A} }$