How many sides does a circle have?

One day, John and his friends were playing around. Jacob hit something with a Pin and it popped. John's dad came into the room that very moment, but he wasn't mad. In fact, he was smiling. What did Jacob hit?

What have one eye but still cannot see?

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

I am weightless, but you can see me. Put me in a bucket, and I'll make it lighter. What am I?

I know a nine-letter word having only one vowel.
Do you ?

I’m tall when I’m young, and I’m short when I’m old. What am I?

What has many keys but can’t open a single lock?

He does not have any heart but still, He manages to live.
If you kill him, you will eventually die but yet you kill him.
He cannot run, who is He?

Count The number of F's in the paragraph below:

"FINISHED FILES ARE THE RESULT OF YEARS OF SCIENTIFIC STUDY COMBINED WITH THE EXPERIENCE OF YEARS"