1917 

 PHYSICS 



Friday 2 p.m. Two hours 



Answer ten questions as indicated below. No extra credit will be given for more 

 than ten questions. Indicate clearly your reasoning in each problem and state the imits 

 in which each answer is expressed. 



Group I 



(Omit one question from this group.) 



1. State Archimedes' principle. Describe an experimental proof of this principle. 



Good eggs sink and bad eggs float in pure water, though the dimensions of 

 the eggs do not change. Explain. 



2. A child weighing 75 pounds sits in a swing. The swing is drawn aside and 



held in equihbrium by a horizontal force of 30 pounds. Find the tension 

 in each of tlie two ropes of the swing. 



3. An automobile tire contains an inner tube, initially empty, the capacity 



of which is 750 cubic inches. A pump, which takes in at each stroke 30 

 cubic inches of air at a pressure of 15 pounds per square inch, is employed 

 to pump up the tire. Assuming no change in temperature, what is the 

 air pressure in the tire after 135 strokes of the pump ? 



4. A rifle weighing 8.7 pounds discharges a bullet weighing 0.32 ounce with a 



velocity of 2,700 feet per second. 



(a) What is the kinetic energy of the bullet ? 



Q)) With what velocity does the gun recoil ? 



Group II 

 {Omit one question from this group.) 



5. What are the nature and the direction of the motions of a small portion of a 



medium which is transmitting sound? 

 A vibrating tuning fork held vertically near the ear is slowly rotated about 

 its shank as an axis. State and explain the effects observed. 



6. What is the length of a pipe, closed at one end, which at 0°C. will give the 



greatest reinforcement to the sound of a tuning fork making 250 vibrations 

 per second ? 



Group III 



{Omit one question from this group.) 



7. Describe two experiments which indicate that heat is a form of energy. 



What causes the draught of a chimney ? 



8. A 30-foot steel rail, when subjected to a change in temperature from — 14°C. 



in winter to 36°C. in summer, changes 0.0195 foot in length. Find the 

 coefficient of linear expansion of steel. 



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