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 The groove around the moon (Posted on 2002-05-06)
Imagine you would have to put a rope around the moon. Since the moon is 1,738,000 metres in diameter, this is a hard task. Finally you have managed to get the rope around the moon but... it is one meter short.

You decide to dig a groove all around the moon, so that the shorter rope suffices. How deep must this groove be? (Assume the Moon to be a perfect sphere.)

 Submitted by charl Rating: 2.9167 (12 votes) Solution: (Hide) The outline of a circle is always 2 * Pi * R (R = the radius). Therefore, the radius will have to decrease by: 100 centimetres / (2 * Pi) = 100 / 6,28 = R = 15,92 cm. So, to put the cable tightly around the moon the groove should be 15,92 centimetres deep. Which is still a huge task if you want to gid this deep all around the moon. The fun thing is, that the depth of the groove does not depend on the radius of the object you are digging it in. You could as well 'dig a groove' in the globe on your desk: it would still have to be 15,92 centimetres.

 Subject Author Date A different (and simple) approach JayDeeKay 2015-06-05 18:08:30 re(2): answer K Sengupta 2008-06-07 16:32:10 re: answer Dej Mar 2008-06-07 12:38:51 answer K Sengupta 2007-05-15 04:19:42 re: Zero Option Solution owl 2004-10-28 12:42:37 Zero Option Solution CeeAnne 2004-10-27 15:28:24 Differences bob909 2004-10-27 09:44:21 re: dig it prashant 2004-03-29 07:52:16 dig it prashant 2004-03-29 07:39:08 Solution Antonio 2003-08-24 03:16:48 No Subject Lucifer 2003-03-01 09:12:26 No Subject danny 2002-11-12 17:42:33 You win Mike 2002-07-24 22:53:55 re: Got to be wrong! TomM 2002-07-24 07:34:23 Got to be wrong! Mike 2002-07-24 05:25:51 My Answer Tom 2002-05-09 12:47:14 thanks John Ryder 2002-05-09 08:04:52 Well... levik 2002-05-08 20:22:10 I understand what you're saying...but John Ryder 2002-05-08 13:08:49 Look at it this way levik 2002-05-08 11:34:48 I don't understand the Solution John Ryder 2002-05-08 07:11:38 Solution Stuff N. Things 2002-05-07 17:55:53 ring around the WHAT? Dan Dise 2002-05-07 13:45:41 But.... John 2002-05-07 12:28:11 solution? John Ryder 2002-05-07 11:45:39 But only... John 2002-05-07 10:43:32 Interesting observation Whiskey Pete 2002-05-07 09:29:50 Hmmm... Tim 2002-05-07 08:59:17 Solution Terry 2002-05-07 08:58:34 David Rowley Correct toferc 2002-05-07 07:37:16 Solution? David Rowley 2002-05-07 07:17:42 1 meter?? kevin 2002-05-07 07:07:13

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