Why Aeroplane windows are round?

I sleep during the day and fly at night, but I have no feathers to aid my flight. What am I?

Can you find the missing piece of the Porsche?

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

John is pretty weird. He likes toffees but hates chocolates. He loves books but never reads. He likes to build his troops in an online game but does not proceed with the war. He likes to go swimming but is afraid of water.

Seeking this behaviour, can you tell whether he likes balloons and parties?

You can win me and lose me but never buy me
You can not eat me and never want to part with me
I can make you cry or bring you joy
I am not a machine and definitely not a toy
You keep me but i am not forever just yours
You might find me in a case or on a shelf next to a vase
I am hard and i am tall if you bump me i am sure to fall
I am made of different materials and am at many events
If your lucky and fight hard I might be yours
What am I ?

What breaks yet never falls, and what falls yet never breaks?

When Jack was six years old he hammered a nail into his favourite tree to mark his height. Ten years later at age sixteen, Jack returned to see how much higher the nail was. If the tree grew by five centimetres each year, how much higher would the nail be?

How many Watermelons are there in the below picture?

They came out at night, without being called.
They lost at day, without being stolen.
Who are they?