Steel wire of length 'L' at `40^(@)C` is suspended from the ceiling and then a mass 'm' is hung from its free end. The wire is cooled dowa from `40^(@)C" to "30^(@)C` to regain its original length 'L'. The coefficient of linear thermal expansiou of the steel is `10^(-5)//^(@)C`, Young's modulus of steel is `10^(11)N//m^(2)` and radius of the wire is 1 mm. Assume that `L gt gt` diameter of the wire. Then the value of 'm' in kg is nearly

Options

A. 1
B. 2
C. 3
D. 4

Answer

C

Explanation

Change in length `Delta L =(MgL)/(YA) = L alpha Delta T therefore m~~3 kg`.
Correct choice : (c ).