A tensioned steel cable of stiffness k k\,k is stretched by a force FFF. The stretching force is suddenly released, and the cable contracts back to its unstretched length in a time interval t t\,t as it performs work.
What is the average power developed by the cable during this contraction?
F22kt\frac{F^2}{2kt}2ktF2
kF22t\frac{k F^2}{2t}2tkF2
F2kt\frac{F^2}{kt}ktF2
F2kt\frac{F}{2kt}2ktF
