Simple riddles with simple answers

An infinite number of mathematicians are standing behind a bar. The first asks the barman for half a pint of beer, the second for a quarter pint, the third an eighth, and so on. How many pints of beer will the barman need to fulfill all mathematicians' wishes?

What gets wet while it's drying?

What has hands but can not clap?

I am full of holes but I can still hold water. What am I?

What has 4 wheels and flies?

If you had a pizza with crust thickness 'a' and radius 'z', what's the volume of the pizza?

I'm in your phone. Sometimes I laugh. Sometimes I cry. I even flip you off from time to time. What am I ?

Two men are in a desert. They're both wearing backpacks. One of the men is dead. The man who is alive, has his pack open. The dead man's pack is closed. What is in their packs?

What letter is a drink?

A natural state, I'm sought by all. Go without me and you shall fall. You do me when you spend, and use me when you need to eat to no end.