20. As 390 g of hot milk cools in a mug, it transfers 30,000 J of heat to the environment. What is the temperature change of the milk? The specific heat of milk is 3.9 J/g·°C

21.  Thermal conductors don’t have to be hot to transfer heat. According to Ch.16, explain a situation when an ice cube would still transfer heat to another object it is in contact with. 

22. What is a medium