Questions and discussion for this lecture live here. Fire away by hitting Reply below 
Well, I took a totally different route and got the same answer, so I guess I am doing okay with this. I went the route of solving for the forces at the hinge joint, F, by taking the sum of moments about B and A. Thank you for creating this solid content!
May be worth driving the point home about how the integral of shear can show moment. I use the concept that the area under the shear curve always correlates to the change in the moment. It serves as a solid double check to assure moments about the cut were calculated correctly. For example. If one found the shear between F and G in this example, we would get the area under the curve equal to 600 kNm, and since we know that F is a pin, then we know that the magnitude of moment should be 600 kNm at the joint G. I have noted that this works well for magnitude of change… but with frames, it is a bit harder to tell where the tension side is with just the shear diagram. Your way of cutting is much better at indicating which joint is the tension side (not to mention how it is much more useful for the moment distribution method for indeterminate frames!). Nonetheless, the area under the shear line/curve can help with the double checking.
Can’t hurt to have the extra tool in the toolbox!
Again. Solid content. Well worth the lifetime membership!
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