Physics Help Forum Mirrors! I need help I have a quiz tonight!
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 Apr 24th 2015, 07:24 AM #1 Junior Member   Join Date: Apr 2015 Posts: 1 Mirrors! I need help I have a quiz tonight! I have a physics test tonight and I really need help with this one problem! This is what I've tried: Your sister is standing in front of a convex mirror, trying on ninja masks. The distances dsister is 46.9 inches. The distance from the mirror to the virtual image is 13.35 inches. What is the distance from your sister to the mirror's focal point, in inches? Give your answer to three decimals. (1/di+1/do)^-1=f > (1/46.9+1/13.35)^-1=10.39195029747 f+do=57.29195029747 The Practice Quiz answer is 65.562. Am I skipping a step? Update: dsister is do Last edited by fisikschick; Apr 24th 2015 at 07:39 AM.
 Apr 24th 2015, 09:59 AM #2 Senior Member   Join Date: Apr 2015 Location: Somerset, England Posts: 1,035 I made it 65.5". But then, I realised that a virtual image is negative in the lens formula. Last edited by studiot; Apr 26th 2015 at 10:13 AM.

 Tags geometric optics, mirrors, need help!, quiz, tonight

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