6. Stainless steel ball bearings

(p= 8085 kg/m³ and cp = 0.480 kJ/kg.°C) having a

diameter of 1.5 inches are to be quenched in water at

a rate of 750 per minute. The balls leave the oven at

a uniform temperature of 950°C and are exposed to

air at 25°C for a while before they are dropped into

the water. If the temperature of the balls drops to

875°C prior to quenching, determine the rate of heat

transfer from the balls to the air. [MO3]