246 APPLIED SCIENCE 



9. To what stress is the boom of a crane subjected when lifting 

 a load? 



MATERIAL-TESTING 



1. What makes one substance stronger than another? 



2. What is elasticity of a body? 



3. Is it possible to twist, bend, or stretch a body? How may 

 each of these actions take place? 



4. What is meant by a cross-section? 



Problems 



STRESSES 



1. What is the weight supported at A and B in Fig. 101? 



2. Two men carry a weight of 20 Ibs. on a pole, one end of the 

 pole being held by each. The weight is 2 ft. from one end and 3 ft. 

 from the other. How many pounds does each man carry? 



MATERIAL-TESTING 



In the following examples, 271,000 is the breaking load. 



1. A test piece 8 in. long between marks and 1^ in. square 

 shows an ultimate strength of 40,000 Ibs. per square inch. What is 

 the total load required to break it? 



2. What is the ultimate elongation in the above test if the 

 elongation of the whole piece is -fa in.? 



3. The breaking load in a tension test is 300,900 Ibs. If the 

 specimen is 1^ in. in diameter, what is the ultimate strength? 



4. A bar 8 in. between marks is pulled in a testing machine until 

 it measures 8.125 in. just at the breaking point. What is the per 

 cent of elongation? 



6. A piece of boiler plate 16 in. long stretches .0125 in. during 

 a test. What is the per cent of elongation? 



6. The unit elongation of a piece in tension is T -J- in. What is 

 its ultimate elongation? 



7. If a cast iron bar 1^ in. X 2 in. breaks under a tension of 

 60,000 Ibs., what tension will break a bar of the same material 

 1 in- in diameter? 



