19. A small dog is trained to jump straight up a distance of 1.2 m. How much kinetic energy does the 7.2-kg dog need to jump this high?

19. A small dog is trained to jump straight up a distance of 1.2 m. How much kinetic energy does the 7.2-kg dog need to jump this high? (The acceleration due to gravity is 9.8 m/s2.) Show your work for credit.

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. Show your work for credit.

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?

Explain why the speed of sound is faster in solids than in gases. Include two other factors Chapter 17 says the speed of sound can depend on.

26.  Which waves have wavelengths longer than those of visible light? Give an example of how each kind of wave is used.

27. According to Chapter 18, explain why a purple flower appears purple when white light shines on it.