At \( 40^{\circ} \mathrm{C} \), a brass wire of \( 1 \mathrm{~mm} \) radius is hung from the ceiling. A small mass \( M …

At \( 40^{\circ} \mathrm{C} \), a brass wire of \( 1 \mathrm{~mm} \) radius is hung from the ceiling. A small mass \( M \) is hung from the free end of the wire. When the wire is cooled down from \( 40^{\circ} \mathrm{C} \) to \( 20^{\circ} \mathrm{C} \), it regains its original length of \( 0.2 \mathrm{~m} \). The value of \( M \) is close to [Coefficient of linear expansion and Youngs modulus of brass are \( 10^{-5} /{ }^{\circ} \mathrm{C} \) and \( 10^{11} \mathrm{~N} / \mathrm{m}^{2} \) respectively, \( g=10 \mathrm{~ms}^{-2} \) ]