Hello,

We know that,

Young's Modulus = Stress / Strain

Stress = Force / Area = F / ( 0.25π x 1^2)

So, Stress = F / 0.785

Now, Strain = Change in Length / Original Length

So, Strain = 1 / 3140

So, Young's Modulus = ( F / 0/785 ) / ( 1 / 3140 )

We know that for steel, Young's Modulus = 2 x 10^5 N / mm^2

So, 2 x 10^5 = ( F / 0.785 ) / ( 1 / 3140 )

So, F = 50 N

Hence, 50 N load is required to hung from end of the steel wire to produce an elongation of 1mm

Best Wishes.