Ballast Sample Problem #3

[design8d]

The section modulus for the cross section of a member is related to the
I moment of inertia of the cross section
II depth of the cross section
III bending stress in the member
IV modulus of elasticity of the member

Answer: I and II only

How is it not I, II and III?

Isn't section modulus directly related to bending stress. Fb = Mmax/S

[Mike-SE]

You do not need to know the bending stress to determine the section modulus but you do need the other two.
A wood 2x4 and a steel 2x4 have the same Ix and Sx but very different Fb.