A metal ball of radius 0.1 m at a uniform temperature of 90Â°C is left in air at 30Â°C. The density and the specific heat of the metal are 3000 kg/m 3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m 2 .K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60Â°C is

A metal ball of radius 0.1 m at a uniform temperature of 90Â°C is le

1.	A metal ball of radius 0.1 m at a uniform temperature of 90Â°C is left in air at 30Â°C. The density and the specific heat of the metal are 3000 kg/m 3 and 0.4 kJ/kg.K respectively. The heat transfer co-efficient is 50 W/m 2 .K Neglecting the temperature gradients inside the ball, the time taken (in hours) for the ball to cool to 60Â°C is
A.	555
B.	55.5
C.	0.55
D.	0.15
Answer» E.

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