lateral thinking - A rope-cutting problem

Here's another oldie from a book, slightly paraphrased to make it more quantitative.

You're in a room with a ceiling exactly 100 feet high. Two thin but sturdy ropes are hanging from fixed hooks at the ceiling and just touch the ground, close enough that you can grab both of them at the same time comfortably. You can climb these ropes, but there is nothing else to climb on. Equipped with only a knife, how much of the rope can you cut down and still end up on the ground unharmed if you can only fall 20 feet without injuring yourself?

Answer

All 200 feet, as long as they're no more than 100 feet apart.

Take one end of one rope. Climb up the other. Tighten the first rope as much as possible, cut (or unhook) the one you just climbed up (keep ahold of it) and swing on the intact rope. Climb to the top of that one. Put the cut rope through the hook. Tie yourself a harness of some sort on one end of it, keep hold of the other, and cut/unhook the rope originally there (again keeping hold of it). Lower yourself down until you are near the end of the rope you are attached to. Tie the spare rope to the end of it, and keep lowering yourself. Once within your safe fall zone, undo the harness and let go that side of the rope, and once you're down pull it through the hook.

As it has been clarified that "the hooks are close enough that you can comfortably reach both of them," the description can be somewhat simplified. Climb up rope A, unhook B, tie it into a harness and re-hook it (such that you can lower yourself), unhook A and continue as above (lower halfway, tie A to the end of B, lower the rest of the way).