Topic:

This is a tricky puzzle question I thought up some time ago, but I figured I would blog it.

As people who study physics know, the acceleration a falling body undergoes if dropped (in a vacuum) at the surface of the earth is known as "g", or 9.8 meters per second per second.

This is so close to 10 that most students and people doing back of envelope calculations often use 10 as the value of a "g". It's easy. Fall for one second and you're going 10 meters/second.

So I got to wondering, how much would the earth have to change to make "g" equal to 10 instead of 9.80665?

So here's the puzzle. By what ratio would you have to increase the diameter of the Earth so that the people on this bigger planet would have "g" equal to 10? Assume the average density of the Earth remains the same (5.46 g/cc).

Then click to the Puzzle Answer

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