Agricultural Education — Examination Papers, 1874. xcL 



EXAMINATION IN MECHANICS AND NATUEAL 

 PHILOSOPHY. 



MAxniuM Number of Marks, 200. Pass Number, 100. 



Tuesday, April lithjfrom 10 a.m. till 1 p.m. 



1. Give the rule for finding the centre of gravity of two heavy points. 

 Draw on your paper a square ABCD, and let the diagonals AC, BD 

 intersect in E ; masses of 2 lbs. and 3 lbs. are placed at A and B 

 respectively : show where a mass of 10 lbs. must be placed that the 

 centre of gravity of the three masses may be at E. 



2. What is meant by the accelerative effect of a force ? The units 

 of distance and time being feet and seconds, it is found that the 

 accelerative effect of a certain force on a body is represented by the 

 number 15 ; what is indicated by this number ? 



3. A lever is supported in a horizontal position on two points, one 

 under each end, 10 feet apart ; a weight of 30 lbs. is hung from it, at 

 a distance of 3 ft. from one point ; find the pressure on each point. 



4. Explain what is meant by the sensibility of a balance. Other 

 things being the same the sensibility is greater as the arms are longer. 

 Why is this ? 



5. A mass weighing 500 lbs. moves at the rate of 50 ft. a second ; 

 what number of units of work is it capable of doing against a resis- 

 tance, by whose action it is brought to rest ? 



6. Explain how the specific gravity of a liquid can be determined 

 by a common hydrometer. A mark [P] is put on the stem of a hydro- 

 meter showing its immersion in a liquid whose specific gravity is 1. ; 

 a second mark [Q] is put on the stem, showing its immersion in a liquid 

 whose specific gravity is 0'8 ; the stem is of uniform thickness, and Q 

 is 4 in. above P. The hydrometer is now placed in a third liquid and 

 is found to sink to a point E, which is 2 in. above P ; what is the 

 specific gravity of the third liquid ? 



7. Find the force which must act along the piston rod to work a 

 common suction pump. Diameter of piston is 6 in., distance between 

 spout and water in well 20 ft. ; what is the required force ? 



8. If a dish of sulphuric acid and a small vessel of water are put 

 under a receiver and the air exhausted, it is found that in a short time 

 the water is converted into ice ; explain the action which takes place, 

 and the part played by the sulphuric acid. 



9. Show by a pen sketch the arrangement of the governor and 

 throttle- valve of a steam-engine ; explain the action of the instrument, 

 and state why the balls should be of considerable weight. 



