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 M = 2m, then the stress produced in the wire is:

For a standard Atwood machine with masses $$M$$ and $$m$$, the formula for the tension in the string/wire upon release is:

$$T = \frac{2Mm}{M + m}g$$ (can be derived by solving the force equation for both the blocks)

$$T = \frac{2(2m)m}{2m + m}g = \frac{4m^2}{3m}g = \frac{4mg}{3}$$

$$\text{Stress} = \frac{\text{Tension}(T)}{\text{Cross-sectional Area}(A)}$$

$$\text{Stress} = \frac{\frac{4mg}{3}}{A} = \frac{4mg}{3A}$$