The time span for which insect can see its image?

  • #1
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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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  • #2
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using laws of reflection.
How did you use the laws of reflection? Remember, the insect has to be able to see its own image.
 
  • #3
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yah to see its own image, i thought it has to be below the mirror.
 
  • #4
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i thought it has to be below the mirror.
Where below the mirror?
 
  • #5
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Where below the mirror?
Yah! I thought so, but i dont know for where it can see its image.
 
  • #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)?
 
  • #7
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can you please say from where ant is able to see its own image? so that i can try the question again!
 
  • #8
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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)?
I think it should be 90 degrees so that is see its own image
 
  • #9
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Very good. Where on the x-axis can you arrange 90 degree incident angles with the mirror?
 
  • #10
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i did a small mistake now i get it! Thanks for the help!
 

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