Consider a section y metres from top. Diameter at this section is
![](https://www.sarthaks.com/?qa=blob&qa_blobid=1041776187913180857)
At this section, moment is given by
M = 600 y N-m
= 600000 y N-mm.
Equating moment of resistance to moment at the section, we get
f Z = M
where f is extreme fibre stress
![](https://www.sarthaks.com/?qa=blob&qa_blobid=3782258246034340546)
![](https://www.sarthaks.com/?qa=blob&qa_blobid=975914406346473564)
Stress at this section f is given by
![](https://www.sarthaks.com/?qa=blob&qa_blobid=10015944585094877488)