Can anyone help me with this physics question?

Question

Determine the elongation of the rod in Figure P9.11 if it is under a tension of 4.2 103 N.

I am pretty sure I have to use the youngs modulus (F/A=Y changeL/Lo). The Y of Al=7e10 Pa and Y of Cu= 11e10 Pa. I may be off track so any help is much appreciated. The figure for this problem is on the link below. Thanx

http://www.webassign.net/sercp/p9-11.gif

Answer 1

Use the formula for Young's Modulus

Y= (F/A) / (changeL/Lo)

Everything in SI units

You are given Y1 and Y2, F and can calculate A because you are given r. You are given ( L0)1 and (L0)2

Therefor apply Young's modulus formula and solve for change L1 and do it again for change L2

Add the two answers to get the elongation.

Answer 2

You're definitely on the right track.

Rearrange F/A = Y*[ΔL/L(i)]  -->  ÃŽÂ”L = [F*L(i)]/[A*Y] and solve it for ΔL(Al) and ΔL(Cu).  Then add those results to the original lengths to get the final rod length.

You're given the force and lengths, and the cross-sectional area can be found easily (convert the radius to m first).