An oil bath maintained at 40°C with a convective coefficient 500 W/m2·K is used to quench stainless steel spherical ball bearings ( 25 W/m·K, 4.85 x 10-6 m2/s) in order to harden them. Consider a ball bearing of uniform temperature 850°C and a diameter of 40 mm. How long, in seconds, will it take for the surface temperature of the sphere to reach 100°C? What is the corresponding center temperature, in °C?

An athlete swings a ball, connected to the end of a chain, in a horizontal circle. the athlete is able to rotate the ball at the rate of 8.13 rev/s when the length of the chain is 0.600 m. when he increases the length to 0.900 m, he is able to rotate the ball only 6.04 rev/s. (a) which rate of rotation gives the greater speed for the ball? 6.04 rev/s 8.13 rev/s (b) what is the centripetal acceleration of the ball at 8.13 rev/s? m/s2 (c) what is the centripetal acceleration at 6.04 rev/s? m/s2