Answer
$\Delta U=-72.9μJ.$
Work Step by Step
Using Formula, we have
$$
\begin{aligned}
\Delta U & =-\mu_{\mathrm{rod}} B\left(\cos \theta_f-\cos \theta_i\right) \\
& =-(270 \mathrm{~A} / \mathrm{m})(0.06 \mathrm{~m}) \pi(0.003 \mathrm{~m})^2(0.03 \mathrm{~T})\left[\cos \left(34^{\circ}\right)-\cos \left(68^{\circ}\right)\right] \\
& =-72.9 \mu \mathrm{J} .
\end{aligned}
$$
