Shear Force and Bending Diagram. Need help understanding.

[bob29]

Homework Statement

[PLAIN]http://img80.imageshack.us/img80/4476/bendingshearquestion.jpg

Homework Equations

\sumM = 0:
\sumFy = 0:

The Attempt at a Solution

Revising for my finals and going over questions, and would like to understand more clearly how to get the following.

Solution is in the image.
[PLAIN]http://img249.imageshack.us/img249/7237/bendingshearsolution.jpg

When 2<x<5:
I do not understand how to obtain the graph.
Shouldn't the graph be from 0<x<5, since it includes the 2m and reaction force at A?
I also do not know how to obtain the (x-2).

Same when 5<x<7:
I do not understand how to obtain the (7-x) or (9-x) in the moment equilibrium equation.

Hope someone can help.
Cheers,

 

[nvn]

bob29: I drew on your diagram to show you how the (x - 2) and 0.5(x - 2) are obtained. The origin is at point A. The blue line is the section cut. The section cut is located at x, measured from the origin. The (x - 2) and 0.5(x - 2) are measured from the section cut, as I showed in the diagram.

Each diagram, such as 2 < x < 5 m, must show everything to the left-hand side of the section cut. If you omit part of the left-hand end of the beam, then you must add the force and moment at the left-hand-end section cut. Omitting part of the left-hand end of the structure perhaps makes it more confusing. And the diagram is inconsistent. Notice the first two domains in the diagram (0 < x < 2, and 2 < x < 5) show the entire structure to the left of the section cut (the blue line). But then the diagram changes its method, and omits a left-hand portion of the structure in the diagram domains 5 < x < 7, and 7 < x < 9.

You can draw the entire structure to the left-hand side of the section cut (the blue line) for each domain, if you wish. And it would make the solution more clear.

 

[bob29]

Thx much easier 2 understand. Should be able to ace this question if it pops up.

 

[MRMACKIE]

Sorry to dig up an old thread but i had a look at the workings posted by nvn and can see how most forces etc are achieved except the force of 2100N, can someone point out what I've missed. Thanks in Advance :-)