What goes up but never comes down?

I am a five-letter word under you,
Remove the first letter and I am above you,
Remove the second as well and I am around you.

Who am I?

If nine thousand, nine hundred nine dollars is written as $9,909,
how should twelve thousand, twelve hundred twelve dollars be written?

What can run but never walks, has a mouth but never talks, has a head but never weeps, has a bed but never sleeps?

What is the unique property of the following words ?
* Revive
* Banana
* Grammar
* Voodoo
* Assess
* Potato
* Dresser
* Uneven

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.

I am the black child of a white father, a wingless bird, flying even to the clouds of heaven. I give birth to tears of mourning in pupils that meet me, even though there is no cause for grief, and at once on my birth, I am dissolved into air. What am I?

Railroad Crossing, look out for the cars. Can you spell that, without any R's ?

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

Can you write down eight eights so that they add up to one thousand?