Question

The strength of a rectangular beam varies jointly as its width and the square of its depth. If the strength of a beam 12 inches wide by 22 inches deep is 3400 pounds per square inch, what is the strength of a beam 9 inches wide and 18 inches deep?

Answer 1

1. s = kwd^2
3400 = k x 12 x 22 x 22
k = 0.585

2. s = kwd^2
s = 0.585 x 9 x 18 x 18
s = 1705.86 ~ 1706 pounds

Hope this helps