I never stop running even when I standstill. If I am formed by joining two identical bodies together, can you guess who I am?

Before the start of the car race, John and Jacob have the same amount of fuel in their car. With this fuel, John can drive for 4 hours while Jacob can drive five hours.
After a time they realize that the amount of fuel left in John's car is 1/4th of the fuel in Jacob's.

For how long they are racing?

What word is identified by the below rebus?

Your Your Your Your Your
Your Your Your Your Your

It comprises roots which nobody sees,
Much taller than those trees,
Up and up it goes,
Still it never grows?

You measure my life in hours
I serve you by expiring
I vanish faster when I am thin
and slower when I am thick
The wind is my energy
What am I?

It walks on 4 when its young, walks on 2 when it's older, and walks on 3 when its very old?

If there are fifteen crows on a fence and the farmer shoots a third of them, how many crows are left?

Only one color, but not one size,
Stuck at the bottom, yet easily flies.
Present in sun, but not in rain,
Doing no harm, and feeling no pain.
What is it?

What is at the end of a rainbow?

You see a boat filled with people, yet there isn’t a single person on board. How is that possible?