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Homework Help: Solving a convex mirror problem

  1. Mar 24, 2014 #1
    1. The problem statement, all variables and given/known data

    Given the following information: convex mirror, focal length (f) = 12.5 metres, height object (ho) = 5 metres, height image (hi) = 1 metre. Find distance object (do) and distance image (di).

    2. Relevant equations

    1/f = 1/do + 1/di

    Magnification= -hi/ho = di/do

    3. The attempt at a solution

    I found that the magnification is -0.2.

    Rearranging the magnification equation I found that di=-0.2do
    and that

    My intention was to substitute one of the two into 1/f = 1/do + 1/di

    I tried to make the denominators equal after substituting in di=-0.2do however my answer was incorrect.

    Correct answers are do = 50 metres, di = -10 metres

    I don't understand how to mathematically solve this problem. Any help would be greatfully appreciated.
  2. jcsd
  3. Mar 24, 2014 #2
    What was your answer?

    I think your approach was right so maybe you just made an arithmetic mistake.
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