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The Maximum Weight

The Maximum weight that a rectangular beam can support varies jointly as its width and the square of its height and inversely as its length. If a beam 1/3 foot wide, 1/4 foot high, and 17 feet long can support 10 tons, Find how much a similar beam can support if the beam is 3/4 foot wide, 1/3 foot high, and 13 feet long. 

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Robert J. | Certified High School AP Calculus and Physics TeacherCertified High School AP Calculus and Ph...
4.6 4.6 (13 lesson ratings) (13)
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Maximum weight =k W*H^2/L, where k is a constant.
10 = k(1/3)(1/4)^2/17 = k/816......(1)
x = k(3/4)(1/3)^2/13 = k/156 ......(2)
(2)/(1): x/10 = 816/156 = 68/13
x = 680/13 = 52.31 tons <==Answer
Brad M. | STEM Specialist plus Business, Accounting, Investment & EditingSTEM Specialist plus Business, Accountin...
4.9 4.9 (230 lesson ratings) (230)
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Hi again, Theresa -- since the 2nd beam is fatter and shorter, we can expect GREATER load support ... width bigger 9/4x ... ht bigger 4/3x ... h^2 bigger 16/9x ... L smaller 13/17 => bigger load by 17/13 ... expect bigger load of 9/4(16/9)17/13 ...  4(17/13) ... 68/13 ...
5 1/4x ==> 52.5 tons :)