Question

A man is running towards a plane mirror at a speed of $2m{s^{ - 1}}$. How fast does he see himself running towards his image?
A.2m/s
B.4m/s
C.5m/s
D.3m/s

Answer 1

Here in this question we have to keep in mind that the person who is standing in front of the mirror seeing his image is approaching his image at $2m{s^{ - 1}}$. As he is approaching his image, the image is also approaching him at the same speed, so the two speeds will be added.

Complete answer:
Here the person will cover the given amount of distance in the required amount of time at the rate of $2m{s^{ - 1}}$. In reality the person would have the same speed of $2m{s^{ - 1}}$ but he would see himself running towards his image at $4m{s^{ - 1}}$. This is so because the image is also running towards him at the speed of $2m{s^{ - 1}}$ so, both of the velocities would add up ($2m{s^{ - 1}}$ of the person running towards his image +$2m{s^{ - 1}}$ of the image running towards the person =$4m{s^{ - 1}}$). It is an illusion that the person sees himself running towards his image. In actuality the person is running at his original speed of $2m{s^{ - 1}}$. The man is running towards a plane mirror at a speed of $2m{s^{ - 1}}$. Sees himself running towards his image at the speed of $4m{s^{ - 1}}$.

So, Option (B) is the correct answer:

Note:
Here, one can be easily mistaken and give the answer $2m{s^{ - 1}}$ which is the person’s real speed/velocity. One has to read the question carefully to know that in the question it is asked the total speed at which the person sees himself running towards his image.