Question

If a boy moves with a speed v towards mirror, the image, to him, will appear to move with a speed:
A) v towards the mirror
B) v away from the mirror
C) 2v towards the mirror
D) 2v away from the mirror

Answer 1

Hint: Mirror is a flat reflective surface. If an object moves with a speed v towards (or away) from a mirror, the image of the object will also move with a speed v towards the mirror with respect to the object.
Therefore, in these types of questions, we will find the relative velocity of the image towards (or away) from the mirror with respect to the object.

Complete Solution:
If a boy moves with a speed v towards the mirror then its image speed will be (-v). The (-) sign is due to the fact that the image moves towards the boy , i.e., in his opposite direction.
The image velocity with respect to boy is given by-
The relative velocity of image w.r.t boy = Velocity of object - Velocity of image
Velocity w.r.t to boy = $v - ( - v) = 2v$
Hence, the image will appear to move with a speed 2v towards the mirror.

Option C is correct.

Note: Trick: In general, in these types of questions, the speed in the mirror will always be twice the actual speed of the object.
Plane mirrors produce images with many distinguishable characteristics. Images formed by plane mirrors are always virtual, upright, left-right reversed, the same distance from the mirror as the object's distance, and the same size as the object.