# GATE ME 2013 | Question: 30

A steel ball of diameter $60$ $mm$ is initially in thermal equilibrium at $1030^0C$ in a furnace. It is suddenly removed from the furnace and cooled in ambient air at $30^0C$, with convective heat transfer coefficient $h = 20 W/m^2K$. The thermo-physical properties of steel are: density $ρ$ = $7800 kg/m^3$, conductivity $k$ = $40$ $W/mK$ and specific heat $c$ = $600$ $J/kgK$. The time required in seconds to cool the steel ball in air from $1030^0C$ to $430^0C$ is

1. $519$
2. $931$
3. $1195$
4. $2144$

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