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Cover the Center (Posted on 2010-06-04) Difficulty: 5 of 5
Can you cover the center of a unit circle, such a Indi's circular pit?

You have a number (N) of identical planks of length L (0 < L <= 2). The planks have small width and negligible thickness, but very high strength and rigidity. No plank extends outside the circle. Both endpoints of each plank, with the exception of the N-th plank, must rest on either the circle or another plank. Neither weaving of planks nor cantilever designs are allowed. Covering the center means that the N-th plank crosses over the center of the circle.

For a given N, L is the minimum length plank necessary.
Obviously if N=1, then L=2.

What is the smallest L when N=2? N=3? N=4?

For larger N, is there an optimum algorithm to minimize L?

Can you determine a general relationship between N and L?

No Solution Yet Submitted by Larry    
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Comments: ( Back to comment list | You must be logged in to post comments.)
Trying N=4 | Comment 2 of 6 |
My best solution looks sort of like an A with the first chord drawn a across the top.  L is about 1.3354 and the send and third planks lie about .352 from the ends of the first chord.

I haven't managed to find a closed form for L.

  Posted by Jer on 2010-06-04 17:14:45
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