A thin rod having a length of 1m and area of cross-section 3×10−6m2 is suspended vertically from one end. The rod is cooled from 210∘C to 160∘C. After cooling, a mass M is attached at the lower end of the rod such that the length of rod again becomes 1m. Young's modulus and coefficient of linear expansion of the rod are 2×1011Nm−2 and 2×10−5K−1, respectively. The value of M is _______ kg. (Take g=10m s−2 )