Stress along a Beam

X1088LoD

I am using a cantilever beam, guided on one end and fixed on the other, (example 1b from Roark's Formulas for Stress and Strain), I have included the page from the book as an attachment.

I want to determine an equation for the stress along the top of the beam.

The beam is 250 mm long, 3 mm high, 25 mm deep.
The modulus of elasticity E is 68927 N/mm^2
The moment of inertia I is 56.25 mm^4
a = 0

From what I have been able to determine
stress = (M*c)/I
where M is the bending moment, c is the distance from the neutral axis to the proper fibers (therefore this is half of the height, 1.5 mm), and I is the moment of inertia.
The bending moment is outlined in the attached file

Is this correct or am I taking the wrong approach? I appreciate any help.

Attached Thumbnails

 

radou

Well, you wrote down the relation between stress and the bending moment function, so try to work something out.