What can you catch but never throw?

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?

I have a clock(12-hour format) and both the needles of the clock overlap at 12:00.
After how much time, they will overlap again?

A boy was at a carnival and went to a booth where a man said to the boy, "If I write your exact weight on this piece of paper then you have to give me $50, but if I cannot, I will pay you $50." The boy looked around and saw no scale so he agrees, thinking no matter what the carny writes he'll just say he weighs more or less. In the end the boy ended up paying the man $50. How did the man win the bet?

There is one four-digit whole number n, such that the last four digits of n2 are the original number n

What number does the below three word/phrase identify and why?
1. Deck
2. Year
3. Singing in the Rain

I am written with two letters.
I said with the one.
I usually am seen with the two.

Who am I?

There was a minor accident with a doctor's son but the doctor noticed no major injury. After the treatment, the father of that doctors son is sitting with the son of the doctor without the doctor being in the room.

How can this be possible?

Two batsman each on 94 runs. Seven runs needed to win in last 3 balls. Both make 100*. How?

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