Physics Question from JEE Main 2026 · 22 January, Shift 2

Two masses $m$ and $2m$ are connected by a light string going over a pulley (disc) of mass $30m$ with radius $r = 0.1 \, \text{m}$. The pulley is mounted in a vertical plane and is free to rotate about its axis. The $2m$ mass is released from rest and its speed when it has descended through a height of $3.6 \, \text{m}$ is _____ $\text{m/s}$. (Assume string does not slip and $g = 10 \, \text{m s}^{-2}$).