2. A boy stands 10 m in front of a plane mirror . then be moves 3 m towards the mirror. How many metres does his image move towards him? A) 20 B) 14 C) 7 D) 6

1 Answer
Jan 24, 2018

D.6

Explanation:

The image formed in a plane mirror is as far behind the mirror as the object is in front of it, i.e. the distance between the object and the mirror u is the same as the distance between the mirror and the image v.

So,here,given u= 10 hence v=10 so distance between the image and the boy is u+v or 20 meters.

If the boy moves 3 meters towards the mirror,then, u=10-3 or 7
So,v =7 as well

Now,distance between the boy and his image is 7+7 i.e 14 meters.

So,the image moved to him by (20-14) or 6 meters

Alternatively,
From the above discussion,clearly,

v+u=x(let)=2u
So, x=2u
Or, (dx)/(dt) = 2(du)/(dt)

It means velocity of image should be twice than that of man's velocity,so if the man moves by 3 m then the image will move to him by 6 m