Answer:
An iron horse with a flaxen tail. The faster the horse runs, the shorter his tail becomes.
What goes with a car, comes with a car, is no use to a car but a car cannot move without it?
I'm not man's best friend, I'm their enemy, I can mark your end, yet you do not see me, I am very small, but very tough, If you have me, then you have it rough.
The stack just might be sent all over. Full of what's new, yet it's nearly obsolete.
Large as a mountain, small as a pea, Endlessly swimming in a water-less sea.
I'm the source of all emotion but I'm caged in a white prison.
Difficult
Animal
Easy
Food
Funny
Kids
Logic
What am I?