50 PROBLEMS IX STRENGTH OF MATERIALS 



475. A wroughtH.ron shaft 20 feet long and 5 inches in diameter is 

 twisted through an angle of 2. Find the maximum unit-stress in 

 the metal. 



476. Find the diameter and angle of twist of a 12-foot wrought-iron 

 shaft transmitting 20 H.P. at 25 R.P.M., with a factor of safety of 6. 



477. A structural steel shaft 120 feet long and 16 inches in diam- 

 eter transmits 8000 H.P. at 20 R.P.M. Find the angle of twist and 

 the factor of safety. 



478. A turbine transmits 92 H.P. at 114 R.P.M. through a wrought- 

 iron shaft 8.5 feet in length. Determine the diameter of the shaft so 

 that the angle of torsion shall not exceed 1. 



479. A structural steel shaft 20 feet in length and 3 inches in 

 diameter transmits 50 H.P. at 200 R.P.M. Through what angle is 

 the shaft twisted and what is the factor of safety? 



480. A structural steel shaft 2 inches in diameter transmits 25 H.P. 

 at 100 R.P.M. Find the factor of safety and the angle of twist per 

 linear foot. 



481. A cast-iron shaft in a spinning mill is 84 feet long and trans- 

 mits 270 H.P. at 50 R.P.M. Find its diameter if the stress in the 

 metal is not to exceed 5000 pounds per square inch and the angle of 

 torsion is not to exceed 0.1 per linear foot. 



482. Determine the diameter and angle of twist of a solid steel 

 shaft 20 feet long, to transmit 6000 H.P. at 116 R.P.M., the maxi- 

 mum twisting moment being 30 per cent greater than the mean and 

 the maximum allowable stress 10,000 pounds per square inch. 



483. Find the size of a hollow steel shaft to replace the one of 

 Problem 482, if the inside diameter is | of the outside diameter. 

 What is the saving in weight in 50 feet of shafting ? 



484. Find the diameter and angle of twist per linear foot of a hollow 

 steel shaft transmitting 5000 H.P. at 70 R.P.M., if the external diam- 

 eter is twice the internal and the maximum stress is 7500 pounds 

 per square inch. 



485. Find the ratio of the strengths of two solid circular shafts of 

 the same material, and the ratio of their stiffness for the same length. 



486. Solve Problem 485, if one diameter is twice the other. 



487. The external diameter of a hollow shaft is n times the internal. 

 Compare its torsional strength with that of a solid circular shaft of 



