22 ANSWERS TO PRACTICAL QUESTIONS 



1 1. What distance should there be between the threads of a 

 screw, that a Po/2$ Ids., acting on a handle 3 //. long, may 

 lift i ton weight? 



F : W : : Interval : Circumference. 



25 Ibs. : 2000 Ibs. : : x : 72 in. x 3.1416. 



x = 2.83 -in. 



12. How high could a P of 11 Ibs., moving i6//. along an 

 inclined plane, lift a W 'of '96 Ibs.? 



P : W : : height : length. 



12 Ibs : 96 Ibs. : : x : 16 ft. 



x = 2 ft. 



13. / wish to roll a barrel of flour into a wagon, the box of 

 which is 4//. from the ground. I can lift but 24 Ibs. How 

 long a plank should I get? 



P : W : : height : length. 

 24 Ibs : 196 Ibs. : : 4 ft. : x = 32 2 / 3 ft. 



14. The " evener" of a pair of whiffletrees is ^ft. 6 in. long , 

 how much must the whiffletree be moved to give one horse the 

 advantage of \ over the other ? 



For every 3 Ibs. one horse pulls, the other must pull 4 Ibs. : hence 7 represents 

 the proportion in which the load is to be divided. 3 ft. 6 in. = 42 inches. 42 

 in. -*-7 = 6 inches, the unit of measure. Hence one arm of the evener must be 

 6 in. x 3 = 18 in. long, and the other 6 in. x 4 = 24 in. long. Or, if we prefer, we 

 may say 21 in. 3 in. = 18 in. Ions:, and 21 in. + 3 in. = 24 in. long. PROOF.- 

 (See Prob. 4, p. 20.) 18 x 4 = 24 x 3 = 72. 



15. In a set of three horse whiffletrees, having an " evene-r" 

 5//. long, at what point should the plough-clevis be attached 

 that the single horse may draw the same as each one of the 

 span of horses ? 



For every Ib. drawn by the single horse the span should draw 2 Ibs. : hence 

 3 represents the proportion in which the load is to be divided. 60 hi. + 3 = 20 

 in., the unit of measure. 20 in. x 1 = 20 in., and 20 in. x 2 = 40 in. Hence eno 

 arm mast be 20 in., and the other 40 in. long. 



To give \ advantage ? 



The single horse should draw 3 Ibs. and each of the others 4 Ibs. : hence the 

 span should draw 8 Ibs. 60 in. +- 11 = 5 6 /n in., the unit of measure. 5/n in. 

 x 3 = 16/ii in., and 5 6 /u in. x 8 = 43 7 /n in. 



1 6. What W can be lifted with a P of 100 Ibs. acting en a 

 screw having threads \ of an inch apart and a lever handle 4 

 //. long? 



