Problem 4: Linkage hinged at one end with an external moment...A linkage is supported by a hinge at A and a cable applied to a spur at C. External loads of 3 and 5 kN are applied at B and D. Draw the shear and bending moment diagrams for the linkage ABCD.

Solution: The free body diagram for the entire beam is:

Now I take a free body diagram of a portion of the beam a distance x from the left end to find the internal force (shear) V and the internal moment M there. I show these in their standard positions (shear is positive down and the moment is positive counterclockwise).
 

	This is the original free body, without Ax, since that force has no effect on the stress due to bending.
	This is a free body taken using a cut between A and B.  V = 8 kN and M = 8x kN-mm (x is in mm).
	This free body was taken using a cut between B and C; therefore, it includes the 3 kN force at B. V = 5 kN and M = 5x + 150 kN-mm
	The cut here is between C and D, thus including the external moment of 80T = 800 kN-mm. Using the sum of the forces and the sum of the moments about the right end (the cut), V = 5 kN and M = 5x - 650 kN-mm

The plots are: