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[ Information | Background | The CyberTeaser | Quantum News | Miscellaneous Stuff ] Solution to CyberTeaser B178
The inside coin travels a distance 12c – 8r, where c is its circumference and r = c/2(pi) is its radius. So it makes 12 – 4/(pi) [approximately 10.7] revolutions. CyberTeaser Archive
Copyright © 1996 National
Science Teachers Association |
As a coin rolls a
distance equal to its circumference, it makes one full revolution. The perimeter of the
rectangle is 12 circumferences. So the outside coin will make 12 revolutions as it rolls
along the rectangle’s sides. In addition, at every vertex of the rectangle it makes
an additional quarter turn (see the figure at right). So the total number of revolutions
for the outside coin is 13. 
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