ELASTIC DEFORMATION 7 



fourth the elastic limit. What is the elongation of the bar -due to the 

 load and that due to its own weight? 



63. A vertical wrought-iron bar 60 feet long and 1 inch in diam- 

 eter is fixed at the upper end and carries a load of 4000 pounds at 

 the lower end. Find the factors of safety for both ends and the 

 elongation of the bar. 



64. Find the length of a vertical wrought-iron rod fixed at its 

 upper end, if the maximum unit-stress in the rod is 8000 pounds 

 per square inch. What will be its elongation ? 



65. Determine the elongation and factor of safety of a vertical 

 structural steel rod 1 inch in diameter and 50 feet long, under its 

 own weight and a weight of 20,000 pounds suspended from its 

 lower end. 



66. A wrought-iron bar 20 feet long and 1 inch square is under a 

 tension of 20,000 pounds. Find the changes in length, section area, 

 and volume. 



67. A structural steel cylinder 2 feet high and 2 inches in diam- 

 eter bears a compressive load of 90,000 pounds. Find the changes 

 in length, diameter, section area, and volume. 



68. A bar of structural steel 4 inches square and 20 feet long is 

 under a tension of 216 tons. Calculate the changes in length, section 

 area, and volume. 



69. A wrought-iron bar is 20 feet long at 32 F. How long will 

 it be at 90F.? 



70. A wrought-iron bar 18 feet long and 1^- inches in diameter is 

 heated to 400 F.; nuts on its ends are then screwed up so as to bear 

 against the walls of a house which have fallen away from the per- 

 pendicular. Find the pull on the walls when the bar has cooled to 

 300 F. 



71. A wrought-iron bar 2 square inches in cross-section has its 

 ends fixed immovably between two walls when the temperature is 

 60 F. What pressure will be exerted on the walls when the temper- 

 ature is 100F.? 



72. Steel railroad rails, each 30 feet long, are laid at a temperature 

 of 40 F. What space must be left between them in order that their 

 ends shall just meet at 90F.? If the rails had been laid with their 

 ends in contact, what would be the unit-stress in them at 90F. ? 



