What goes up but never comes down?

Solve the puzzle by telling what does below picture means.

A Scientist was fifty years old in the year 2000 but he was forty years old in the year 2010. How can this be possible?

PS: It has a logical answer.

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

Here is what you have to do. You have to throw a ball as hard as you can but it must return back to you even if it does not bounce at anything. Also, you have nothing attached to the ball. There is no one on the other end to catch that ball and throw it back at you.

How will you do it?

Out of four images which one is the odd one out?

You walk into a room that contains a match, a kerosene lamp, a candle and a fireplace. What would you light first?

I cannot talk, but I always reply when spoken to. What am I?

Can you find the missing number in the third row?
35 20 14
27 12 18
5 2 ?

Place the numbers from 1 to 9 in the circles in a manner that each side of the triangle sums up to 17.