1917 

 Comprehensive Examination 



PHYSICS 



Monday, September 17 2-5 p.m. 



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

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

 examination. 



Answer ten numbered questions, distributed as follows: three from Group I, two from 

 Group II, two from Group IV, two from Group V, and one of the remaining questions. 



The nimiber in parenthesis before each question indicates the number of credits 

 assigned to it. 



Show clearly the method by which you obtained your answers to problems and state 

 the units used in each case. 



Attach to the answer, in each case, the number and letter used in the printed paper. 



Table of Constants 



Acceleration of gravity =980 cm. per sec. per sec. 

 1 horse-power = 746 watts. 



Group I 



1. a) (5) A 100-lb. child in a swing is pushed 9 ft. away from the vertical, the 



distance from the top of the swing to the center of gravity of the 

 child being 15 ft. What horizontal force is necessary to hold him 

 in his new position ? 

 b) (5) What is the strain on each of the swing ropes ? 



2. a) (6) A uniform plank 20 ft. long weighing 50 lbs. rests on a support 6 ft. 



from one end. The plank is held in a horizontal position by a verti- 

 cal rope attached to the other end of the plank. What is the force 

 on the support and the tension in the rope ? 

 b) (4) How far from the support can a boy of 80 lbs. walk before the plank 

 tips ? ]\Iake a diagram. 



3. A box weighing 200 lbs. is pushed up a plank 10 ft. long into a wagon 4 ft. 



high. Disregarding friction: 



a) (3) What force is necessary to keep the box from sliding down the plank ? 



b) (2) What work is done in pushing the box from the ground into the wagon ? 



If a force of 30 lbs. is required to overcome friction: 



c) (3) What is now the total work done ? 



d) (2) What is tlie efficiency in this case ? 



4. a) (3) State the principle of the conservation of energy. 



b) (7) A 142-gm. baselmll is dropped from the Washington monument, a 

 distance of 160 m. If tliis ball is caught and is stopped within a 

 distance of 80 cm., what is the average force it will exert upon the 

 catcher's hand ? Neglect the resistance of the air. 



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