Question: Fifty is my first, my second is the third in fourth, and my end is the end of an ending. With a nut I become a nut that isn't, and without one I move.
Answer: Lug. Roman numerals for fifty is L, the third letter in fourth is U, and the end of ending is G. With a nut is Lug nut, which is a nut in one sense, but isn't a nut like an almond. Without nut Lug has a similar meaning to tug, which is moving stuff.
Question: A semi truck weighing exactly 10,000 pounds gets onto a bridge that is 100 miles long. The bridge's weight limit is exactly 10,000 pounds, any more will break the bridge. After going about 80 miles down the bridge a small bird lands on the truck.
Answer: Nothing, after traveling 80 miles the truck will have surely burnt enough fuel to allow the bird to land on the truck without breaking the bridge.