How many words can a pen with half refill write?

I am a five-letter word and people eat me. If you remove the first letter I become an energy form. If you remove the first two letters, I am needed to live. Scramble the last three letters and I am a drink. What word am I?

John enters a small room. The Door Closes.
When the door opens, John is in a larger room.

Explain?

What has no start, end, or centre?

A man dies of old age on his 25 birthday. How is this possible?

If a boy blows 18 bubbles,
Then pops 6 eats 7 and then
He pops 5 and blows 1.
How many are left?

What time is it when an elephant sits on a fence?

You can see it everyday, But cannot touch it at will. What is it?

I am beautiful, up in the sky. I am magical, yet I cannot fly. To people I bring luck, and to some people, riches. The boy at my end does whatever he wishes. What am I?

A rubber ball keeps on bouncing back to 2/3 of the height from which it is dropped. Can you calculate the fraction of its original height that the ball will bounce after it is dropped and it has bounced four times without any hindrance ?