GATE2017 ME-2: 47

A metal ball of diameter $60$ mm is initially at $220^{\circ}$ C. The ball is suddenly cooled by an air jet of $20^{\circ}$ C. The heat transfer coefficient is $200 W/m^{2}.K$. The specific heat, thermal conductivity and density of the metal ball are $400$ J/kg.K, $400$ W/m.K and $9000 kg/m^{3}$, respectively. The ball temperature (in $^{\circ} C$) after $90$ seconds will be approximately

1. $141$
2. $163$
3. $189$
4. $210$

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