Question

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

Answer 1

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`