
$=\frac{I B_{0} R}{2} \int_{0}^{\pi}(\sin \theta \hat{i}+\cos \theta \hat{j}) x(-\cos \theta \hat{k}) d \theta$
$=\int_{0}^{\pi}\left(\sin \theta \cos \theta \hat{j}-\cos ^{2} \theta \hat{i}\right) d \theta$
$=\int_{0}^{\pi}\left(\frac{\sin 2 \theta \hat{j}}{2}-\frac{(1+\cos 2 \theta) \hat{i}}{2}\right) d \theta$
$=\left[\frac{-\cos 2 \theta}{4}\right]_{0}^{\pi} \hat{j}-\left[\frac{\theta}{2}\right]_{0}^{\pi} \hat{i}-\left[\frac{\sin 2 \theta}{4}\right]_{0}^{\pi} \hat{i}$
$=0-(\pi / 2) \hat i-0=-(\pi / 2) \hat i$

