At 40
o
C, a brass wire of 1 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
o
C to 20
o
C it regains its original length of 0.2 m. The value
of M is close to :
(Coefficient of linear expansion and Young’s modulus of brass are 10
–5
/
o
C and 10
11
N/m
2
, respectively; g=
10 ms
–2
)