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 \begin{aligned} \alpha &=\dfrac{a_{\mathrm{t}}}{r} \\ &=\dfrac{7.14 \mathrm{~m} / \mathrm{s}^{2}}{0.320 \mathrm{~m}} \\  &=22.3 \, \mathrm{rad} / \mathrm{s}^{2}.\end{aligned}