Glass spheres of 2 mm radius and at 500 degree Celsius are to be cooled by expos

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Glass spheres of 2 mm radius and at 500 degree Celsius are to be cooled by exposing them to an air stream at 25 degree Celsius. Find the minimum time required for cooling to a temperature of 60 degree Celsius. Assume the following property values
Density = 2250 kg/m³
Specific heat = 850 J/kg K
Conductivity = 1.5 W/m K

Options:

A . 13.78 seconds

B . 14.78 seconds

C . 15.78 seconds

D . 16.78 seconds

Answer: Option B
Answer: (b).14.78 seconds

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