Calculate initial diameter from longitudinal strain and final diameter

Snoopdork

"Calculate the initial diameter of a wire that has been longitudinally strained by 30% and whose final diameter is 0.1cm. Assume no volume change."

Now I know that if there is no volume change, v=poisson's ratio= 0.5. Thus the lateral strain would equal 30%*0.5= 15%. But when I plug it into the strain equation and use a diameter of 0.1cm as the initial length, I get 0.1176. The answer is supposed to be 0.114cm.

Any thoughts?

mgb_phys

If there is no volume change you don't have to know about wires or poisson ratio.
It's just a simple geometry excercise
pi r1^2 L1 = pi r2^2 L2 and L2 = 1.3 L1 just rearrange in terms of r1

Snoopdork

Wow I way over thought that one, thanks.