Statics: Bending of a beam/evenly distributed force problem

[hattori_hanzo]

Hello, and sorry for my English, as I am Norwegian.

I have a statics problem which I can not understand.

I've taken a pic from my book:

The problem asks me to find the largest bending stress, σ_b, in the incisions 1 and 2.

I have the solution in front of me, I just don't understand what they have done with the evenly distributed force (q). Especially in incision 2, when they find M_b, they have used: M_b = F_A*a_A-q*2.5m*1.25.

The q*2.5m I can understand, but where does the 1.25 come from? I thought it should be divided by 2?

Can someone explain how this works for me?

 

[Studiot]

Especially in incision 2, when they find Mb, they have used: Mb = FA*aA-q*2.5m*1.25.

Please confirm what the symbols stand for.

In particular what is a_A and M_b ?

You have not provided symbols for the reactions at A and B?
Do you know how to calculate these reactions?

You should start by writing the equation for the bending moments for 16.2 and 16.3, using x for the horizontal axis and starting with x=0 at A. Can you do this?
It will have the form M = some function of x and the loads to the left of x.