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What's wrong with CDs? (Posted on 2005-03-30) Difficulty: 3 of 5

The diameter of a long playing vinyl record is 12 inches. The unused center has a diameter of 4 inches, and there is a smooth outer edge that is 1 inch wide. If there are 91 grooves to the inch, how far does the needle travel within the groove during playback of the record?

See The Solution Submitted by Erik O.    
Rating: 4.0000 (1 votes)

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re: Solution | Comment 3 of 10 |
(In reply to Solution by e.g.)

But with a diameter of 12 inches, the radius is only 6 inches.  Subtract out the 2-inch radius of the unused center and you're left with 4 inches. The smooth outer edge is 1 inch wide, so you're left with only 3 inches.  Even if you double it, for the two sides of the record, it's only 6 inches (plus an amount to account for it's being an arc of a circle centered on the pivot of the tone arm, rather than a straight line).

And the category is Calculus, not Tricks.


  Posted by Charlie on 2005-03-30 15:25:19
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