8 PROBLEMS IN STRENGTH OF MATERIALS 



73. A wrought-iron tie-rod 20 feet in length and 2 inches in diam- 

 eter is screwed up to a tension of 10,000 pounds in order to tie to- 

 gether two walls of a building. Find the stress in the rod when the 

 temperature falls 20 F. 



74. A cast-iron bar is confined between two immovable walls. 

 Find the unit-stress that will be produced by a rise in temperature 

 of 50 F. 



75. A structural steel tie-rod 40 feet in length and 2 inches square 

 is subjected to a steady stress of 40,000 pounds. Find the elonga- 

 tion and the number of foot-pounds of work done. 



76. How much work is done in subjecting a cube of 125 cubic inches 

 of wrought-iron to a tensile stress of 10,000 pounds per square inch ? 



77. Find the work which is done in stressing bars of cast-iron, 

 wrought-iron, and structural steel, each 1 inch in diameter and 2 feet 

 long, up to their elastic limits. 



78. Calculate the work which is required to stress a wrought-iron 

 bar 2 inches in diameter and 5 feet long from 6000 to 12,000 

 pounds per square inch. 



79. The work done by a gradually applied force in elongating a 

 1-inch square wrought-iron rod 25 feet long is 100 foot-pounds. 

 What is the magnitude of the force applied ? 



80. A structural steel rod is required to support a suddenly applied 

 load of 10,000 pounds. What is the minimum diameter of the rod 

 if a permanent set is avoided ? 



81. A vertical rod, 2 square inches sectional area, carries a load of 

 5000 pounds. If an additional load of 2000 pounds is suddenly 

 applied, what is the unit-stress produced ? 



82. Steam at a pressure of 50 pounds per square inch is suddenly 

 admitted upon a piston 32 inches in diameter. Find the work done 

 upon the steel piston-rod, which is 4 feet in length and 2 inches in 

 diameter. 



83. A line of steel rails is 10 miles in length when the tempera- 

 ture is 32F. Find the length when the temperature is 102 F. and 

 the work stored up in the rails per square inch of section. 



84. A wrought-iron bar 25 feet in length and 1 square inch in 

 sectional area has its temperature increased 20 F. Determine the 

 work done. 



