Good Riddles

Question: With one you can't count past six,
nor can the gap between v and x be fixed.
You can read all of these lines,
but can't say what solves me.

What am I?

Question: You have 7 tennis balls that are all identical but one of them is slightly lighter than the others.

Using a balance scale and only two separate weightings, how can you find the light tennis ball?

Question: What sport starts with a T, has four letters, and is played around the world?

Question: When do you go at red, but stop at green?

Question: 100 feet in the air, yet its back is on the ground.

What is it?