What has 13 hearts but no other organs?

A train full of passengers goes through a tunnel. When the train comes out from the other end, there is no single person on the train.

How did it happen?

A sundial has the fewest moving parts of any timepiece. Which has the most?

Use the numbers 2, 3, 4 and 5 and the symbols + and = to make a true equation. Conditions: Each must be used exactly once and no other numbers or symbols can be used.

Your last good ping-pong ball fell into a narrow metal pipe embedded one foot deep in concrete.
How can you get it out undamaged, if all the tools you have are your tennis paddle, shoe laces, and plastic water bottle, which does not fit into the pipe?

When I got four, I have it none.
When I got two, I have it some.
When I got none, I have it all.

What is it?

Who always enjoys poor health?

Eight of us go fourth, not back, to protect our king from an attack. What are we?

I am the one who remains awake when you sleep. But I need to rest when you awake. Who Am I?

Four men were in a boat on the lake. The boat turns over, and all four men sink to the bottom of the lake, yet not a single man got wet! Why?