This problem came in an exam . An object is approaching a mirror with a SPEED V . Find the SPEED of the image relative to the object . My solution - The object approaches the mirror with a SPEED V relative to the ground . Thus the image approaches the object with a SPEED V relative to the ground. Since this is SPEED , and NOT VELOCITY we don't give a damn to whether the image is traveling towards or away from the object , and in any case whatsoever the SPEED of the image relative to the object is going to be ZERO. However , if it has been velocity in case of speed , the relative velocity of the image w.r.t object would have been 2V. Most people are saying the answer is 2V. Please enlighten .