________________________________________________________________________ PROBLEM (12.98) A weight W = 25 lb falls a distance h = 4.5 ft when it comes into contact with end B of the steel rod (E = 30 x 106 psi) of length L = 6 ft, as shown in Fig. P12.98. What diameter d should the rod have if the maximum stress is not to exceed 20 ksi? SOLUTION δ st = WL AE σ st = σ max = Kσ st = or [ W 2h [1 + 1 + ] A δ st σ max A W W A − 1]2 = 1 + 2h δ st or 2 σ max A 2σ max A W 2 − W +1 = 1+ 2hAE WL Solving A= 2W hE + σ max ] [ 2 W σ max 2(25) 4.5 × 12(30 × 106 ) [ = + 20 ×103 ] = 2.815 in.2 3 2 (20 ×10 ) 6 ×12 Therefore, πd2 = 2.815 , d = 1.893 in. 4 Excerpts from this work may be reproduced by instructors for distribution on a not-for-profit basis for testing or instructional purposes only to students enrolled in courses for which the textbook has been adopted. Any other reproduction or translation of this work beyond that permitted by Sections 107 or 108 of the 1976 United States Copyright Act without the permission of the copyright owner is unlawful.