Answer
$2.64cm$
Work Step by Step
We can find the diameter of the copper rod as
$d_{cu}=\sqrt{\frac{(\frac{Q_{total}}{t})(\frac{4L}{\pi \Delta T})-K_{pb}d_{pb}^2}{K_{Cu}}}$
We plug in the known values to obtain:
$d_{Cu}=\sqrt{\frac{(33.2)\frac{4(0.650)}{\pi(112-21)}-(34.3)(0.0276)^2}{395}}$
$d_{Cu}=2.64cm$
