3. A certain wire, 3 m long, stretches by 1.2 mm when under tension of 200 N. By how much does
an equally thick wire 6 m long, made of the same material and under the same tension, stretch?

The extension of the second wire is  

Explanation:

From the question we are told that

    The length of the wire is

     The elongation of the wire is  

        The tension is

       The length of the second wire is  

Generally the Young's modulus(Y) of this material is  

Where

    Where A is the area which is evaluated as  

  and  

   So

Since the wire are of the same material Young's modulus(Y)  is constant

So we have  

Now the ration between the first and the second wire is

Since tension , radius are constant

   We have

substituting values

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