igid 



Comprehensive Examination 



PHYSICS 



Monday, September i8 2:00-5:00 p.m. 



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

 of the examination, imless a 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) Define kinetic energy; potential energy. 



b) A shell weighing 6 lbs. fired from an anti-aircraft gun aimed vertically 

 upward has a muzzle velocity of 1,200 ft. per sec. If the shell bursts 

 beside an aeroplane 3 sec. after leaving the gun, how high is the 

 aeroplane ? 



2. A boy weighing no pounds sits in a hammock whose ropes make angles of 



60° and 30° respectively with the horizontal. Find the tension in each 

 rope. 



3. a) Draw a diagram of a force pump. Explain the action of the pump, 



referring as much as possible to your diagram in giving your explana- 

 tion. 

 b) A 1.5 horse-power gasoUne engine is used to drive a force pump which 

 pumps water from a spring to a 60-gallon tank 70 ft. higher than the 

 spring. If the tank is filled in 2 minutes, what is the efficiency of the 

 pump ? (A gallon of water weighs 8 . 4 lbs.) 



4. A bubble has a volume of 5 c.c. and is at a depth of i meter below the surface 



of water, the barometer reading 70 cm. of mercury. If the barometric 

 pressure changes to 73 cm., what will be the resulting volume of the bubble ? 

 (Specific gravity of mercury =13. 6.) 



5. Explain the action of a megaphone. Give a physical explanation of the 



reason that sound can be transmitted to greater distances through a 

 speaking-tube than in the open. Why does the presence of a large 

 number of people in an auditorium improve its acoustic properties, that 

 is, make it easier to understand the speaker? 



6. a) The sound of a fire-alarm is heard 3 sec. after the bell is struck by the 



hammer. If the temperature of the air is at 68° F., how far away is 

 the bell? 

 b) If the A above middle C, tuned to 435 vibrations per second, is the standard 

 pitch for the orchestra, what is the vibration frequency of middle C 

 upon the same scale ? 



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