HBH Logical 6: Space Rock

Logical challenge #6 in Hellbound Hackers is called “Space Rock”:

Suppose you are working for the science department and the NASA brought you a rock from space and before you are supposed to do anything with it you need to get the volume. But in your office you only have a pencil, a ruler and a glass of water and of course the rock. Using only those things, how can you get a close estimate of the volume of the rock?

This is such a classic puzzle that everyone should know it. Especially those who are in fourth grade or higher. The principle to be used is called “Archimedes Principle”, named after a Greek intelligent guy called Archimedes. He laid down in his bathtub, when he noticed the water around him rising. Get it yet?

Do the following, assuming that the rock fits into the glass, the glass is a cylinder and the water won’t flow over:

1. Mark the water level on the glass with the pencil.
2. Put the rock in the glass.
3. Measure the difference between the new water level and the old one.
4. Measure the radius of the glass.
5. Calculate the volume of the rock: r²*pi*dh where r is the radius of the glass, pi is about 3.14 and dh is the change in the water level.

I’m just wondering why NASA don’t have better equpiment, why they give the stone to some office guy and WHY they allow him to wet it.

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