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Log in a river

  1. Oct 9, 2008 #1
    1. The problem statement, all variables and given/known data

    Two rivers of unequal width (64m and 125m) meet at a right angle, forming an L-shaped channel. What is the longest possible log you can float on it?

    2. Relevant equations

    3. The attempt at a solution
    I tried for equal widths and built a recursive algorithm for turning the log. But it is getting stuck if the log is [tex]2\sqrt{2}(Width)[/tex]
  2. jcsd
  3. Oct 9, 2008 #2
    the log will turn around the inner corner. just find a formula for finding the length of a line entirely in the water which passes through that point. then find the minimum
  4. Oct 10, 2008 #3


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    Staff Emeritus
    Science Advisor

    Start by drawing a picture. Draw two channels of width 64 and 125 and draw a straight line from the outside edges just touching the inside corner. You should be able to find a formula for the length of that line in terms of x, the distance from the outside corner to one of the ends of the line. Then find x which minimizes length. You MIGHT be able to get that by completing the square but I seem to remember a problem like this requiring a derivative. Are you sure this is "precalculus"?
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