196 



RESISTANCE OF MATERIALS 



291. Three smooth cylindrical water mains, each weighing 600 lb., are placed in 

 a wagon box, two of them just filling the box from side to side and the third being 

 placed on top of these two. Find the pressure between the pipes and also against 

 the bottom and sides of the wagon. 



292. An engine is part way across a bridge, the weights and distances being as 

 shown in Fig. 136. Find the reactions of the abutments. 



79 



j'o" 



5'0" 



lO'o" 5'0" 



I 



64-0 



FIG. 136 



FIG. 137 



293. In the letter scales shown in Fig. 137 the length of the parallel links is 

 3 in., and the distance of the center of gravity of the moving parts below the pivot 

 is 2 in. If the radius of the scale is 8 in. and the weight of the moving parts is 

 12 oz., find the distance between successive ounce 



graduations on the scale. 



294. A scale is arranged as shown in Fig. 138. 

 Determine the relation between the load and the 

 weight P. (Quintenz scales, Strassburg, 1821.) 



FIG. 138 



FIG. 139 



Solution. With the given dimensions we have, by the principle of moments, 



" 1 e+ d' 



and 

 whence 



Pa = 



p a =Wb-W-(b cV 



l\ e + d / 



