If you say my name, I will no longer exist. What am I?

The Puzzle: A girl, a boy, and a dog start walking down a road.

They start at the same time, from the same point, in the same direction.

The boy walks at 5 km/h, the girl at 6 km/h.

The dog runs from boy to girl and back again with a constant speed of 10 km/h. The dog does not slow down on the turn.
How far does the dog travel in 1 hour?

I am the fastest animal but cannot climb the tree. What am I?

Two in a corner, one in a room, zero in a house, but one in a shelter. What is it?

How many letters are in the alphabet?

I am a type of vehicle that has two wheels and is powered by humans. What am I?
Hint 1: You can ride me for exercise.
Hint 2: I am environment-friendly.

I possess a head

I flaunt a tail

But I don't have mouth or legs

Can you find out who I am?

There are a number of books on a shelf. If one book is the 4th from the left and 6th from the right, how many books are on the shelf?

A new Engineering building containing 100 offices had just been completed. John was hired to paint the numbers 1 to 100 on the doors. How many times will John have to paint the number nine (9)?

Can you name any English verb that becomes its past tense by simply rearranging the alphabets ?