I am a seven-letter word but if you remove four of my letters I will have one left. What word am I?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

A man in a car saw a Golden Door, Silver Door and a Bronze Door. What door did he open first?

If an electric train is travelling south, then which way is the smoke going?

I am taken from a mine and shut up in a wooden case, from which I am never released, and yet I am used by almost every person. 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 ?

I have a big mouth and I am also quite loud! I am NOT a gossip but I do get involved with everyone's dirty business.

What does this mathematical rebus means ?

I come in different shapes and sizes.
Parts of me are curved, other parts are straight.
You can put me anywhere you like,
but there is only one right place for me.
What am I?

I am soft and cuddly that soothe your heart. But, If you pick my last name I am going to tear you all apart. Who am I?