EXERCISES 75 



Sources of heat are the sun, fuels, collision, friction, and electrical 

 resistance. 



78. Exercises. 



1. If you mix 100 g. of water at 80 C. with 100 g. of water at C., 

 what temperature will the mixture have? 



2. How many calories are needed to melt 100 g. of ice? If you mix 

 100 g. of water at 80 C. with 100 g. of ice at G., what will happen? 

 What will the temperature of the mixture be? 



3. If a glass fruit jar is filled completely with water, then sealed, 

 and put outdoors in zero weather, what is likely to happen? Why? 



4. If you open the valve of a full bicycle tire, the escaping air feels 

 cold; why? 



5. If steam at 100 C. enters the steam coil of a room, and water at 

 100 C. leaves the coil, how is the room heated? 



6. Why does sprinkling a lawn in hot weather cool the air? 



7. If some liquid air is poured into an open beaker, its temperature 

 does not rise above 182.5 C., no matter how warm the room is. 

 Explain. 



8. What do we mean by saying that the specific heat of water is 9 

 times that of iron? 



9. Why does a nail struck repeatedly with a hammer become hot? 

 Why does a bit used to drill holes in a board become hot? What 

 causes a "hot box" on a railway car? Give other illustrations of the 

 same phenomenon. 



