For clarification, here is an example problem:
A circular steel wire 2 m long must stretch no more than 0.25 cm when a tensile force of 400 N is applied to each end of the wire. What minimum diameter is required for the wire?
FL = YA(ΔL)
Apparently, the cross section area for this object is simply pi*r^2 (as for any circle). Can someone tell me exactly what the cross section area is supposed to refer to? I thought it was the area of the plane of the object perpendicular to the applied force, but apparently I’m wrong or not understanding something properly.