What goes up but never comes down?

I know a nine-letter word having only one vowel.
Do you ?

A famous swimmer can swim downstream in a lake in exactly 40 minutes with the lake current.
He can swim upstream in that lake in exactly 60 minutes against the lake current.
The length of the lake is 2 km.

How long he can cover the distance of one side at a still lake with no current?

How will you measure 15 minutes using two hourglasses of 7 minutes and 11 minutes respectively?

It has five wheels, though often think four, You cannot use it without that one more, You can put things in it, you can strap things on top, You can't find it in the market, but you can still go shop. What is it?

A guard is positioned at the one side of the bridge saying ‘A’. His task is to shoot all those who try to leave from ‘A’ to the other side and say ‘B’. He also need to welcome the person who comes from another side ‘B’ to his side ‘A’. The guard comes out of his post every 1 hour and looks down the bridge for any people trying to leave. You are at side ‘A’ and wish to go to another side ‘B’. you also know that it would take 1:45 hr to cross the bridge. How will you cross the bridge?

By removing one matchstick and adding one matchstick, can you convert the word "ZOO" to an animal name?

Can you find out which number multiplied by itself will give the output as 12345678987654321?

When you say goodbye, I am what you need to tie.
I come as a couple and go wherever you run.
Who am I?

What does this mean?

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