A 160mm stick is set in equilibrium on a block, as shown. Setting fire to its right extremity, and knowing

that the fire burns, each minute, 10mm of the stick into ash, calcule how long the stick stays in equilibrium on the block.
http://www.flickr.com/photos/80147355@N0…

Well, presumably, to begin with, the stick is placed symmetrically on the block, so there is 50 mm on each side of the block, which means that the block is 60 mm wide.

The stick will reach tipping point when there is 50 mm left lying on the block, exactly balancing the 50 mm overhang at the left.

This will happen when 60 mm have burnt away. And at 10 mm per minute, this will take 6 minutes.


[ In fact, it does not matter what width the block is. The stick will remain in equilibrium as long as the unburnt portion is longer than 50 mm to counteract the 50 mm overhang. So tipping point is always when the length of the stick has been reduced by 60 mm, regardless of the size of the block.]

typos- *calculate
*without the block's
*

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