What will be the image speed if
(i) Object is moving towards the plane mirror with speed v ?
(ii) The plane mirror is moving towards the object with speed v ?

Explanation

(i) If object displaces by an amount x towards the mirror, image also displaces by the same amount towards the mirror. Thus if objects velocity is v towards the mirror, image's velocity is also v towards the mirror.

(ii) Let the mirror move towards the object by distance x. Let d be the original distance between the object and the mirror.

`rArr 2d` = Distance between O and l.
and 2d - 2x = Distance between O and l'.
`rArr` As mirror moves towards the object by amount x, image moves towards the object by amount 2x.
Hence, velocity of the image is 2v in the same direction as that of the mirror.