A solid circular flywheel disk is 0.025 m thick, has density 7800 kg/m³ and central mass moment of inertia 4.36 kg·m². Find its radius in m to two decimals.
Mass is $m=\rho\pi r^2t$ and polar mass inertia is $I=mr^2/2$. Hence $r=[2I/(\rho\pi t)]^{1/4}=[8.72/(7800\pi\times0.025)]^{1/4}\approx0.345$ m. Rounded radius: **0.35 m**.
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