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The time span for which insect can see its image?

  1. Feb 7, 2015 #1
    1. The problem: A plane mirror of length 2m is kept along the line y=-x as shown in the figure. An insect having velocity of 4 766b43090560fe2b414b4100dcbfbac3.png cm/s is moving along x-axis from far away. The time span for which the insect can see its image will be:


    A)50 sec B)25 sec C)25√2 sec D)50√2 sec


    2.The answer given is D-50√2 sec

    3. The attempt at a solution: I've tried to solve it by using laws of reflection. but i cant get the answer that is given from the options. So please help!

    My solution was : the insect can see its image form the bottom of the mirror ie., for 2m for x-axis . so the time span is 2m=200 cm
    time span= 200/4=50sec
    but why is the answer 50√2 .
    Have i done anything wrong?
     

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    Last edited by a moderator: Apr 19, 2017
  2. jcsd
  3. Feb 7, 2015 #2

    Bystander

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    How did you use the laws of reflection? Remember, the insect has to be able to see its own image.
     
  4. Feb 7, 2015 #3
    yah to see its own image, i thought it has to be below the mirror.
     
  5. Feb 7, 2015 #4

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    Where below the mirror?
     
  6. Feb 7, 2015 #5
    Yah! I thought so, but i dont know for where it can see its image.
     
  7. Feb 7, 2015 #6

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    What's the angle of incidence for light from the insect to strike the mirror and return to the insect's eye(s)?
     
  8. Feb 7, 2015 #7
    can you please say from where ant is able to see its own image? so that i can try the question again!
     
  9. Feb 7, 2015 #8
    I think it should be 90 degrees so that is see its own image
     
  10. Feb 7, 2015 #9

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    Very good. Where on the x-axis can you arrange 90 degree incident angles with the mirror?
     
  11. Feb 7, 2015 #10
    i did a small mistake now i get it! Thanks for the help!
     

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