Internal forces for massless rods in rotation

1. Jan 12, 2012

euprax

Lets say we have a mass attached to a rigid, massless rod that is fixed at the other end, so we have a system that can only undergo rotation. My question is, if we apply a force to the rigid rod (and not to the actual mass), how can we derive (using only F=Ma) the shear force distribution in the rod so that the forces applied to the ends will produce the expected angular acceleration.

It seems like I can get this answer using conservation of angular momentum or conservation of energy, but I cannot see how I could use only free body diagrams and F=Ma to detemine that, for example, applying a force midway through the rod will result in only half the force being transmitted to the mass at the end of the rod.

Again, I know how to get the answer, but I cannot visualize what is happening with the internal forces to make such a result come about.

Thanks!!