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Q: A solid steel sphere (AISI 1010), 300 mm in diameter, is coated with a dielectric material layer of thickness 2 mm and thermal conductivity 0.04 W/m' K. The coated sphere is initial1y at a uniform temperature of 500°C and is suddenly quenched in a large oil bath for which T? = 100°C and h = 3300 W/m2 · K. Estimate the time required for the coated sphere temperature to reach 140°C.