IIT JEE Advanced 2011 Paper 1

The change in length is
ΔL =

FL

YA

F = mg
The change in length due to the change in temperature is ΔL = LαΔT
where α is the coefficient of linear expansion and ΔT is the change in temperature.
α = 10−5∕°C , Y =

1011N

m2

The radius of wire is 1 mm. Therefore,
A = π×10−6m2
Now,

FL

YA

= LαΔT
That is, mg = YAαΔT
Therefore,
m =

011×3.14×10−6×10−5×10

9.8

= 3.2 kg ~ 3 kg