Chapter 30 - Electromagnetic Induction - Exercises and Problems - Page 871: 27

$U = 7.9\times 10^{-4}~J$

We can find the stored energy: $U = \frac{1}{2}~L~I^2$ $U = (\frac{1}{2})~(\frac{\mu_0~N^2~V}{L^2})~(I^2)$ $U = (\frac{1}{2})~(\frac{\mu_0~N^2~\pi~r^2}{L^2})~(I^2)$ $U = (\frac{1}{2})~[\frac{(4\pi\times 10^{-7}~H/m)~(200)^2~(\pi)~(1.5\times 10^{-2}~m)^2}{(0.12~m)^2}~]~(0.80~A)^2$ $U = 7.9\times 10^{-4}~J$