On 10-20, I think I may be missing an important part of the problem. If I need to find the force exerted by table on the chain at any instant (in terms of W, the weight of the chain already on the table at that moment), I don't see why the table should be considered to be exerting any force on the part of the chain that is still in the air. What important link am I missing here?
Ahem, a missing 'link' in the 'chain' problem. Hrrrrm.
When each link in the chain hits the table it undergoes an inelastic collision with table. Therefore the table is exerting a force on the chain equal to the weight of the chain on the table plus the time rate of change of total momentum of the chain (F = dp/dt).