A man stands 10 m in front of a large plane mirror. How far must he walks before he is 5 m away from his image?

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neela's profile pic

neela | High School Teacher | (Level 3) Valedictorian

Posted on

In a plane mirror the image is virtual. It appears the same distance behind the mirror as the object is in front and that is the law of reflection.

Therefore, to have 5 meter distance between him and the image, the virtual distance of the virtual image behind the mirror should be equal to the real distance between the man and mirror .  Therefore the man sholul stand 5/2 meter before the mirror to have 5 feet distance between him and his image. That meanes he should walk by another 7.5 meter towards the mirror  in a direction perpendicular to the mirror surface or along the line of man and image line. 

krishna-agrawala's profile pic

krishna-agrawala | College Teacher | (Level 3) Valedictorian

Posted on

The distance of an object from its image in a plane mirror is exactly double the distance of the object from the mirror.

Thus for the man to be 5 meters away from his image he should be at a distance half of that>

Therefore required distance of man from mirror = 5/2 = 2.5 m

Original distance of man from mirror = 10 m (given)

Difference in original and required distance = 10 - 2.5 = 7.5 m.

Therefor:

The man must walk 7.5 m towards the mirror to be 5 m away from his image.

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