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 valuesDensity = 2250 kg/m3Specific heat = 850 J/kg KConductivity = 1.5 W/m K

• A. 13.78 seconds
• B. 14.78 seconds
• C. 15.78 seconds
• D. 16.78 seconds