Elasticity,stress, and strain questions

[defdek]

1. A 3.0-mm2 cross sectional area metal rod is stretched by 0.4 mm when a certain stretching force is applied to it. Another rod of the same length and metal but of a cross sectional of twice as large is stretched by the same amount of force. Calculate the stretching in the second wire.

the answer is 0.2mm? half stretch than the first rod?

2.Compute the strain energy stored in an aluminium wire of 2.0 m long, 1.0 mm diameter subjected to a 25.0-N tension. [Y-aluminium = 7.0 x 10^10 Nm-2].
i just have to use this formula right?
F^2L/2AY

3.A stretched wire has strain energy per unit volume of 4.00 x 10^3 Jm-3. Find the Young’s modulus and the stress in the wire if the wire elongates 0.5% of its original length.
i have no idea about this
1/2Y(strain)^2 ?

 

[nvn]

(1) Excellent work, defdek. Your answer on question 1 is correct.

(2) Nice work on question 2. That is correct.

(3) <standing ovation. crowd roars.> Nice job on question 3. That is correct.