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Nearsightedness and Plane Mirrors

  1. Apr 21, 2008 #1
    1. The problem statement, all variables and given/known data
    A 13.0 foot long, nearsighted python is stretched out perpendicular to a plane mirror, admiring its reflected image. If the greatest distance to which the snake can see clearly is 29.0 ft, how close must its head be to the mirror for it to see a clear image of its tail?

    3. The attempt at a solution
    I tried the obvious and easiest approach which of course yields an incorrect answer. Seems to me to just take 29-13. Obviously the nearsightedness comes into this problem somewhere, but I don't know how to use that information to obtain an answer.
  2. jcsd
  3. Apr 22, 2008 #2


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    Hi negatifzeo,

    Let's say the snake's head is some distance d from the mirror, so that in this problem d is what we want to find. The snake is stretched out straight away from the mirror; what is the distance from the snake's tail to the mirror? Where is the location of the image of it's tail?

    Once you have that, remember that if the snake wants to see the image of its tail, the image must not be any farther than 29 ft from its eyes. What then does d need to be so that it can see the image of the tail?
  4. Apr 22, 2008 #3


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    Hi negatifzeo! :smile:

    I can't add anything to what alphysicist has said, except:

    :smile: ALWAYS DRAW A DIAGRAM! :smile:
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