318 PRACTICAL MATHEMATICS 



(20) Find the intensity of the shear stress at the neutral axis, 

 if the section Fig. 73, No. 8, is subjected to a shearing force of 

 1000 Ib. 



(21) If the section Fig. 73, No. 9, is subjected to a shearing 

 force of 5000 Ib., what is the intensity of the shear stress at the 

 neutral axis, and what fraction is it of the average shear stress 

 for the whole section ? 



(22) A hollow circular section, external radius 5 inches, internal 

 .radius 3" inches, is subjected to a shearing force of 2000 Ib. What 

 is the intensity of the shear stress at the diameter ? 



(23) What is the diameter of a steel shaft which will stand a 

 twisting moment of 16,000 inch pounds, the maximum shear stress 

 being 10,000 Ib. per sq. inch ? If a hollow steel shaft of 4 inches 

 external diameter will stand the same twisting moment, what is 

 its internal diameter ? If the length of each shaft is 9 ft., what 

 is the angle of twist in each case ? N = 13 x 10 6 Ib. per sq. inch. 



(24) A hollow steel shaft is subjected to pure twisting and 

 transmits 5000 H.P. at a speed of 95 revolutions per minute. If 

 the shear stress must not exceed 10,000 Ib. per sq. inch and the 

 internal diameter is to be 75 per cent, of the external diameter, 

 find the external diameter. 



