(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

i had a solid rectangular beam of max stress equalling 1.65x10^6N/m²

a new beam, a hollow rectangular beam is made to reduce weight, it has the same maximum bending stress 1.65x10^6N/m² but this time has a horizontal dimension of 0.2m and a constant wall thickness of 0.02.

i need to find the vertical dimension but am really having trouble rearranging the formula

M=550

2. Relevant equations

I=B.D^3/12 - b.d^3/12

max stress = MY/I

3. The attempt at a solution

1.65x10^6 N/m²= 12X550/(BD^3-bd^3)

then

(BD^3-bd^3)=12x550/1.65x10^6

having trouble getting the D value to equal a calculation

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# Homework Help: How to rearrange to find the height of a hollow beam

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