I9i6 



Comprehensive Examination 



PHYSICS 



Friday, June 23 9:00 a.m.-i2:oo m. 



A teacher's certificate covering the laboratory instruction must be presented as part 

 of the examination, unless the laboratory notebook is to be presented at a laboratory 

 examination. 



Answer ten questions. Show clearly the method by which you obtain your answers, 

 and state the units used in each case. 



1. a) What is meant by potential energy ? by kinetic energy ? Give examples. 

 h) A body whose mass is 50 gm. is raised to a height of 300 cm. What is 



its potential energy ? 



c) If it is allowed to fall freely, what will be its potential energy after it has 



fallen through a distance of 100 cm. ? What is its kinetic energy at 

 this point ? What is the sum of these two energies ? 



d) After it has fallen through the whole distance, 300 cm., what is its kinetic 



energy ? 



e) What principle do the combined answers to (6), (c), and {d) illustrate ? 



2. Define coefficient of friction; mechanical advantage. 



A boat weighing 1,800 lbs. is to be drawn to a point above high water level 

 along a beach which rises 3 ft. in 10 ft. Make a sketch of a six-rope block 

 and tackle adapted to the foregoing purpose, and calculate the force 

 required, assuming the coefficient of friction between the boat and the 

 beach to be 0.4, 



3. Given a U-tube and some water: {a) explain how you would determine the 



pressure of the illuminating gas in the pipes of a house; {b) explain how 

 the result may be reduced to pounds per square inch. (One cubic foot 

 of water weighs 62 .4 lbs.) 



4. A standard life-preserver made of cork, the specific gravity of which is o. 14, 



measures 40 in. X 1 2 in. X 2 in. ; what extra weight would the life-preserver 

 support when completely immersed in sea-water of specific gravity 1.03. 

 State the principle involved in the solution of the problem, (i cu. ft. of 

 fresh water weighs 62.4 lbs.) 



5. The vibration frequency of two equal strings 5 ft. long is 236 vibrations per 



sec. How many beats per sec. will be heard when one of the strings has 

 been shortened i inch ? 



6. Describe fully a laboratory experiment for determining the rate of vibration 



of some body emitting a sound. 



7. What is the source of the heat which melts the ice in a tightly closed refriger- 



ator ? If it requires 3 lbs. of ice to cool a gallon of milk (8 . 3 lbs.) con- 

 tained in a glass jar weighing 4 lbs., from 75° F. to 40° F., what is the effi- 

 ciency of the refrigerator ? Assume specific heat of milk to be i . o, specific 

 heat of glass to be o. 12, and the latent heat of melting of ice to be 147 in 



the units here used. 



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